Triangle Seminars
July 2023
Wed
12 Jul 2023
Entanglement entropy in internal space and Holography
๐ London
Sumit Das
(Kentucky)
Abstract:
Most realizations of holography in String Theory involve space-times of the form of AdS X Y, where Y is an internal space which geometrizes R symmetries. The initimate connection of bulk reconstruction in AdS with the entanglement of subregions of the base space of the dual field theory suggests the possibility that a reconstruction of the internal space could be related to entanglement among internal degrees of freedom. We initiate an investigation into this issue by studying properties of RT surfaces which are smeared along the AdS directions, and anchored on the boundary of a subregion of the internal space Y. In cases where the product space appears as an IR geometry of a higher dimensional asymptotically AdS space we identify the area of the RT surface with the entanglement entropy associated with an operator subalgebra, and speculate on stand alone instances of product spaces.
Most realizations of holography in String Theory involve space-times of the form of AdS X Y, where Y is an internal space which geometrizes R symmetries. The initimate connection of bulk reconstruction in AdS with the entanglement of subregions of the base space of the dual field theory suggests the possibility that a reconstruction of the internal space could be related to entanglement among internal degrees of freedom. We initiate an investigation into this issue by studying properties of RT surfaces which are smeared along the AdS directions, and anchored on the boundary of a subregion of the internal space Y. In cases where the product space appears as an IR geometry of a higher dimensional asymptotically AdS space we identify the area of the RT surface with the entanglement entropy associated with an operator subalgebra, and speculate on stand alone instances of product spaces.
Posted by: andrea
Thu
6 Jul 2023
Do black holes have a horizon?
๐ London
Daniel Terno
(Macquarie University)
Abstract:
For a distant observer with finite lifetime the main characteristic a black hole is trapping of light. Semiclassical description of black holes and especially the logical basis for construction of exotic horizonless models are based on two common but usually implicit assumptions. The first is a consequence of the cosmic censorship conjecture, namely that curvature scalars are finite at
apparent horizons. The second is that horizons form in finite asymptotic time (i.e. according to distant observers), a property implicitly assumed in conventional descriptions of black hole formation and evaporation. On the other hand, traversable wormholes are required to form in finite time and to be sufficiently regular by their design specifications.
Taking these as the only requirements within the semiclassical framework, one finds that in spherical symmetry only two classes of black/white hole solutions are admissible: each describing only evaporating black holes and expanding white holes. I review their properties and present the implications. For example, the null energy condition is violated in the vicinity of the outer and satisfied in the vicinity of the inner apparent/anti-trapping horizon. A test particle falls into a black hole in a finite time (according to a distant clock), and it is possible to be swallowed by a white hole. Kerr-Vaidya black holes share these qualitative features.
I conclude by discussing how the recent observation suggest that black holes are horizonless objects, and why some potential models of such objects, like wormholes, are ruled out.
For a distant observer with finite lifetime the main characteristic a black hole is trapping of light. Semiclassical description of black holes and especially the logical basis for construction of exotic horizonless models are based on two common but usually implicit assumptions. The first is a consequence of the cosmic censorship conjecture, namely that curvature scalars are finite at
apparent horizons. The second is that horizons form in finite asymptotic time (i.e. according to distant observers), a property implicitly assumed in conventional descriptions of black hole formation and evaporation. On the other hand, traversable wormholes are required to form in finite time and to be sufficiently regular by their design specifications.
Taking these as the only requirements within the semiclassical framework, one finds that in spherical symmetry only two classes of black/white hole solutions are admissible: each describing only evaporating black holes and expanding white holes. I review their properties and present the implications. For example, the null energy condition is violated in the vicinity of the outer and satisfied in the vicinity of the inner apparent/anti-trapping horizon. A test particle falls into a black hole in a finite time (according to a distant clock), and it is possible to be swallowed by a white hole. Kerr-Vaidya black holes share these qualitative features.
I conclude by discussing how the recent observation suggest that black holes are horizonless objects, and why some potential models of such objects, like wormholes, are ruled out.
Posted by: andrea
Wed
5 Jul 2023
VOAs and RG flows in 4D N=2 Theories
๐ London
Jacques Distler
(University of Texas Austin)
Abstract:
4D N=2 theories exhibit a rich structure of RG flows between UV and IR SCFTs. With G. Elliot, M.J. Kang and C. Lawrie, we have been this structure of RG flows from a variety of perspectives. In this talk, I would like to focus on the Vertex Operator Algebra (VOA) that can be associated to a 4D N=2 SCFT, and what these VOAs can tell us about the Higgs Branch RG flow between these theories.
4D N=2 theories exhibit a rich structure of RG flows between UV and IR SCFTs. With G. Elliot, M.J. Kang and C. Lawrie, we have been this structure of RG flows from a variety of perspectives. In this talk, I would like to focus on the Vertex Operator Algebra (VOA) that can be associated to a 4D N=2 SCFT, and what these VOAs can tell us about the Higgs Branch RG flow between these theories.
Posted by: andrea
June 2023
Wed
28 Jun 2023
Numerical experiments on coefficients of instanton partition functions
๐ London
Aradhita Chattopadhyaya
(Dublin Institute of Advanced Studies)
Abstract:
We analyze the coefficients of partition functions of Vafa-Witten theory for the complex projective plane CP^2. We experimentally study the growth of the coefficients for gauge group SU(2) and SU(3), which are examples of mock modular forms of depth 1 and 2 respectively. We also introduce the notion of "mock cusp form'', and study an example of weight 3 related to the SU(3) partition function. Numerical experiments on the first 200 coefficients suggest that the coefficients of a mock modular form of weight k grow as the coefficients of a modular form of weight k, that is to say as n^{k-1}. On the other hand the coefficients of the mock cusp form appear to grow as n^{3/2}, which exceeds the growth of classical cusp forms of weight 3. We provide bounds using saddle point analysis, which however largely exceed the experimental observation.
We analyze the coefficients of partition functions of Vafa-Witten theory for the complex projective plane CP^2. We experimentally study the growth of the coefficients for gauge group SU(2) and SU(3), which are examples of mock modular forms of depth 1 and 2 respectively. We also introduce the notion of "mock cusp form'', and study an example of weight 3 related to the SU(3) partition function. Numerical experiments on the first 200 coefficients suggest that the coefficients of a mock modular form of weight k grow as the coefficients of a modular form of weight k, that is to say as n^{k-1}. On the other hand the coefficients of the mock cusp form appear to grow as n^{3/2}, which exceeds the growth of classical cusp forms of weight 3. We provide bounds using saddle point analysis, which however largely exceed the experimental observation.
Posted by: andrea
Mon
26 Jun 2023
String compactifications, closed differential forms, and mapping cones
Li-Sheng Tseng
(UC Irvine)
Abstract:
In compactifications over smooth geometrical spaces, closed differential forms can take on a prominent role. For instance, closed forms can represent the geometrical structure of special holonomy manifolds and also fluxes that are present in the compactifications. In this talk, we will describe novel geometrical invariants that arise on manifolds with a distinguished closed form. In particular, we will show that there are natural cohomologies of mapping cone type that in general are dependent on the distinguished closed form. These cohomologies provide another tool to help count the massless scalars that arise in compactifications.
In compactifications over smooth geometrical spaces, closed differential forms can take on a prominent role. For instance, closed forms can represent the geometrical structure of special holonomy manifolds and also fluxes that are present in the compactifications. In this talk, we will describe novel geometrical invariants that arise on manifolds with a distinguished closed form. In particular, we will show that there are natural cohomologies of mapping cone type that in general are dependent on the distinguished closed form. These cohomologies provide another tool to help count the massless scalars that arise in compactifications.
Posted by: IC2
Wed
21 Jun 2023
Scalar QED in AdS
๐ London
Lorenzo Di Pietro
(Trieste)
Abstract:
Based on 2306.05551 with Ankur and D. Carmi. Studying QFT in AdS allows to translate phenomena in massive QFT in the bulk to properties of the boundary conformal correlators. I will illustrate this in the example of a strongly coupled gauge theory, namely scalar QED in dimension D<4. The tool that I will use to compute is the large N expansion, where N is the number of flavors. I will show that the four-point function of the charged operator dual to the scalar electrons can be computed exactly in the coupling at leading order at large N, both in the Coulomb and in the Higgs phase, and explain its salient properties. Finally I will discuss an IR divergence present in integer dimension D=3 that signals the breaking of the AdS isometries due to a boundary running coupling.
Based on 2306.05551 with Ankur and D. Carmi. Studying QFT in AdS allows to translate phenomena in massive QFT in the bulk to properties of the boundary conformal correlators. I will illustrate this in the example of a strongly coupled gauge theory, namely scalar QED in dimension D<4. The tool that I will use to compute is the large N expansion, where N is the number of flavors. I will show that the four-point function of the charged operator dual to the scalar electrons can be computed exactly in the coupling at leading order at large N, both in the Coulomb and in the Higgs phase, and explain its salient properties. Finally I will discuss an IR divergence present in integer dimension D=3 that signals the breaking of the AdS isometries due to a boundary running coupling.
Posted by: andrea
Tue
20 Jun 2023
A large eta approach to single field inflation (NOTICE THE UNUSUAL TIME)
Gianmassimo Tasinato
(Swansea University)
Abstract:
Single field models of inflation capable to produce primordial black holes usually require a significant departure from the standard, perturbative slow-roll regime. In fact, in many of these scenarios, the size of the slow-roll parameter eta becomes larger than one during a short phase of inflationary evolution. In order to develop an analytical control on these systems, I explore the limit of eta large, and promote 1/eta to a small quantity to be used for perturbative expansions. Formulas simplify, and analytic expressions for the two and three point functions of curvature fluctuations are obtained. I will then discuss the behaviour of loop corrections to inflationary observables in this framework
Single field models of inflation capable to produce primordial black holes usually require a significant departure from the standard, perturbative slow-roll regime. In fact, in many of these scenarios, the size of the slow-roll parameter eta becomes larger than one during a short phase of inflationary evolution. In order to develop an analytical control on these systems, I explore the limit of eta large, and promote 1/eta to a small quantity to be used for perturbative expansions. Formulas simplify, and analytic expressions for the two and three point functions of curvature fluctuations are obtained. I will then discuss the behaviour of loop corrections to inflationary observables in this framework
Posted by: IC
Fri
16 Jun 2023
The mathematics of black holes and spacetime singularities
Mihalis Dafermos
(Cambridge/Princeton)
Abstract:
General relativity makes spectacular predictions about our world, predictions which have captured the popular imagination more than any other part of physics: gravitational waves, black holes, spacetime singularities. For the mathematician, however, perhaps the most spectacular thing about these predictions is not their exoticness, but, on the contrary, the fact that they all correspond to well-defined mathematical concepts: Indeed, it was precisely through mathematics that these predictions of general relativity were first discoveredรขโฌโoriginally to much controversy and objection!รขโฌโand the qualitative mathematical analysis of the Einstein equations remains one of the most powerful ways to understand the great conceptual questions of the theory. This talk will describe some past contributions of mathematics to general relativity and some of the big open conjectures which mathematics hopes to answer in the future.
General relativity makes spectacular predictions about our world, predictions which have captured the popular imagination more than any other part of physics: gravitational waves, black holes, spacetime singularities. For the mathematician, however, perhaps the most spectacular thing about these predictions is not their exoticness, but, on the contrary, the fact that they all correspond to well-defined mathematical concepts: Indeed, it was precisely through mathematics that these predictions of general relativity were first discoveredรขโฌโoriginally to much controversy and objection!รขโฌโand the qualitative mathematical analysis of the Einstein equations remains one of the most powerful ways to understand the great conceptual questions of the theory. This talk will describe some past contributions of mathematics to general relativity and some of the big open conjectures which mathematics hopes to answer in the future.
Posted by: oxford
Thu
15 Jun 2023
Holographic description of code CFTs
๐ London
Anatoly Dymarsky
(Kentucky)
Abstract:
Recently, a relation was introduced connecting codes of various types with the space of abelian (Narain) 2d CFTs. We extend this relation to provide holographic description of code CFTs in terms of abelian Chern-Simons theory in the bulk. For codes over the alphabet Z_p corresponding bulk theory is, schematically, U(1)_p times U(1)_{-p} where p stands for the level. Furthermore, CFT partition function averaged over all code theories for the codes of a given type is holographically given by the Chern-Simons partition function summed over all possible 3d geometries. This provides an explicit and controllable example of holographic correspondence where a finite ensemble of CFTs is dual to "topological/CS gravity" in the bulk. The parameter p controls the size of the ensemble and "how topological" the bulk theory is. Say, for p=1 any given Narain CFT is described holographically in terms of U(1)_1^n times U(1)_{-1}^n Chern-Simons, which does not distinguish between different 3d geometries (and hence can be evaluated on any of them). When p approaches infinity, the ensemble of code theories covers the whole Narain moduli space with the bulk theory becoming "U(1)-gravity" proposed by Maloney-Witten and Afkhami-Jeddi et al.
Recently, a relation was introduced connecting codes of various types with the space of abelian (Narain) 2d CFTs. We extend this relation to provide holographic description of code CFTs in terms of abelian Chern-Simons theory in the bulk. For codes over the alphabet Z_p corresponding bulk theory is, schematically, U(1)_p times U(1)_{-p} where p stands for the level. Furthermore, CFT partition function averaged over all code theories for the codes of a given type is holographically given by the Chern-Simons partition function summed over all possible 3d geometries. This provides an explicit and controllable example of holographic correspondence where a finite ensemble of CFTs is dual to "topological/CS gravity" in the bulk. The parameter p controls the size of the ensemble and "how topological" the bulk theory is. Say, for p=1 any given Narain CFT is described holographically in terms of U(1)_1^n times U(1)_{-1}^n Chern-Simons, which does not distinguish between different 3d geometries (and hence can be evaluated on any of them). When p approaches infinity, the ensemble of code theories covers the whole Narain moduli space with the bulk theory becoming "U(1)-gravity" proposed by Maloney-Witten and Afkhami-Jeddi et al.
Posted by: andrea
Wed
14 Jun 2023
Holographic description of code CFTs
๐ London
Anatoly Dymarsky
(U Kentucky)
Abstract:
Recently, a relation was introduced connecting codes of various types with the space of abelian (Narain) 2d CFTs. We extend this relation to provide holographic description of code CFTs in terms of abelian Chern-Simons theory in the bulk. For codes over the alphabet Z_p corresponding bulk theory is, schematically, U(1)_p times U(1)_{-p} where p stands for the level. Furthermore, CFT partition function averaged over all code theories for the codes of a given type is holographically given by the Chern-Simons partition function summed over all possible 3d geometries. This provides an explicit and controllable example of holographic correspondence where a finite ensemble of CFTs is dual to "topological/CS gravity" in the bulk. The parameter p controls the size of the ensemble and "how topological" the bulk theory is. Say, for p=1 any given Narain CFT is described holographically in terms of U(1)_1^n times U(1)_{-1}^n Chern-Simons, which does not distinguish between different 3d geometries (and hence can be evaluated on any of them). When p approaches infinity, the ensemble of code theories covers the whole Narain moduli space with the bulk theory becoming "U(1)-gravity" proposed by Maloney-Witten and Afkhami-Jeddi et al.
Recently, a relation was introduced connecting codes of various types with the space of abelian (Narain) 2d CFTs. We extend this relation to provide holographic description of code CFTs in terms of abelian Chern-Simons theory in the bulk. For codes over the alphabet Z_p corresponding bulk theory is, schematically, U(1)_p times U(1)_{-p} where p stands for the level. Furthermore, CFT partition function averaged over all code theories for the codes of a given type is holographically given by the Chern-Simons partition function summed over all possible 3d geometries. This provides an explicit and controllable example of holographic correspondence where a finite ensemble of CFTs is dual to "topological/CS gravity" in the bulk. The parameter p controls the size of the ensemble and "how topological" the bulk theory is. Say, for p=1 any given Narain CFT is described holographically in terms of U(1)_1^n times U(1)_{-1}^n Chern-Simons, which does not distinguish between different 3d geometries (and hence can be evaluated on any of them). When p approaches infinity, the ensemble of code theories covers the whole Narain moduli space with the bulk theory becoming "U(1)-gravity" proposed by Maloney-Witten and Afkhami-Jeddi et al.
Posted by: QMW
Wed
14 Jun 2023
The partial Bondi gauge: Further enlarging the asymptotic structure of gravity
๐ London
Celine Zwikel
(Perimeter)
Abstract:
I will introduce the partial Bondi gauge for 4-dimensional spacetimes. This gauge includes the usual Bondi gauge and Newman-Unti gauge and is designed to approach asymptotic boundaries along null rays. The new gauge is defined by three conditions on the metric (g_{rr}=0=g_{rA}) and relaxes the condition on the radial coordinate. I will discuss the solution space and asymptotic symmetries. Most importantly, by relaxing the gauge, we uncover new large symmetries that characterize asymptotically flat spacetimes.
I will introduce the partial Bondi gauge for 4-dimensional spacetimes. This gauge includes the usual Bondi gauge and Newman-Unti gauge and is designed to approach asymptotic boundaries along null rays. The new gauge is defined by three conditions on the metric (g_{rr}=0=g_{rA}) and relaxes the condition on the radial coordinate. I will discuss the solution space and asymptotic symmetries. Most importantly, by relaxing the gauge, we uncover new large symmetries that characterize asymptotically flat spacetimes.
Posted by: andrea
Wed
14 Jun 2023
Line Operators in Chern-Simons-Matter Theories and Bosonization in Three Dimensions
Deliang Zhong
(Tel Aviv U.)
Abstract:
We study Chern-Simons theories at large N with either bosonic or fermionic matter in the fundamental representation. The most fundamental operators in these theories are mesonic line operators, the simplest example being Wilson lines ending on fundamentals. We classify the conformal line operators along an arbitrary smooth path as well as the spectrum of conformal dimensions and transverse spins of their boundary operators at finite 't Hooft coupling. These line operators are shown to satisfy first-order chiral evolution equations, in which a smooth variation of the path is given by a factorized product of two line operators. We argue that this equation, together with the spectrum of boundary operators, are sufficient to determine these operators' expectation values uniquely. We demonstrate this by bootstrapping the two-point function of the displacement operator on a straight line. We show that the line operators in the theory of bosons and the theory of fermions satisfy the same evolution equation and have the same spectrum of boundary operators.
We study Chern-Simons theories at large N with either bosonic or fermionic matter in the fundamental representation. The most fundamental operators in these theories are mesonic line operators, the simplest example being Wilson lines ending on fundamentals. We classify the conformal line operators along an arbitrary smooth path as well as the spectrum of conformal dimensions and transverse spins of their boundary operators at finite 't Hooft coupling. These line operators are shown to satisfy first-order chiral evolution equations, in which a smooth variation of the path is given by a factorized product of two line operators. We argue that this equation, together with the spectrum of boundary operators, are sufficient to determine these operators' expectation values uniquely. We demonstrate this by bootstrapping the two-point function of the displacement operator on a straight line. We show that the line operators in the theory of bosons and the theory of fermions satisfy the same evolution equation and have the same spectrum of boundary operators.
Posted by: IC2
Tue
13 Jun 2023
TBA
Rishi Mouland
(Cambridge U. DAMTP)
Abstract:
TBA
TBA
Posted by: IC
Thu
8 Jun 2023
Information loss, black holes, and algebras in time
๐ London
Nima Lashkari
(Purdue)
Abstract:
A manifestation of the black hole information loss problem is that the two-point function of probe operators in an eternal AdS black hole decays exponentially fast in time, whereas, on the boundary, it is expected to be an almost periodic function of time. We point out that the decay of the two-point function (clustering in time) holds important clues to the nature of observable algebras, states, and dynamics in quantum gravity. In the thermodynamic limit of infinite entropy (infinite volume or large N), the operators that cluster in time are expected to form an algebra. We prove that this algebra is a unique and very special infinite dimensional algebra called the III_1 factor. This has implications for the emergence of a local bulk in holography.
An important example is \mathcal{N}=4 SYM, above the Hawking-Page phase transition. The clustering of the single trace operators implies that the algebra is a type III_1 factor. We prove a generalization of a conjecture of Leutheusser and Liu to arbitrary out-of-equilibrium states. We explicitly construct the C^*-algebra and von Neumann subalgebras associated with time bands and more generally, arbitrary open sets of the bulk spacetime in the strict N\to \infty limit. The emergence of time algebras is intimately tied to the second law of thermodynamics and the emergence of an arrow of time.
A manifestation of the black hole information loss problem is that the two-point function of probe operators in an eternal AdS black hole decays exponentially fast in time, whereas, on the boundary, it is expected to be an almost periodic function of time. We point out that the decay of the two-point function (clustering in time) holds important clues to the nature of observable algebras, states, and dynamics in quantum gravity. In the thermodynamic limit of infinite entropy (infinite volume or large N), the operators that cluster in time are expected to form an algebra. We prove that this algebra is a unique and very special infinite dimensional algebra called the III_1 factor. This has implications for the emergence of a local bulk in holography.
An important example is \mathcal{N}=4 SYM, above the Hawking-Page phase transition. The clustering of the single trace operators implies that the algebra is a type III_1 factor. We prove a generalization of a conjecture of Leutheusser and Liu to arbitrary out-of-equilibrium states. We explicitly construct the C^*-algebra and von Neumann subalgebras associated with time bands and more generally, arbitrary open sets of the bulk spacetime in the strict N\to \infty limit. The emergence of time algebras is intimately tied to the second law of thermodynamics and the emergence of an arrow of time.
Posted by: andrea
Wed
7 Jun 2023
Quantum and Classical Eikonal Scattering
๐ London
Giulia Isabella
(Geneva)
Abstract:
I will discuss the eikonal scattering of two gravitationally interacting bodies, showing that exponentiation of the scattering phase matrix is a direct consequence of the group contraction \(SU(2) \rightarrow ISO(2)\), in the large angular momentum limit. The emergence of the classical limit is understood in terms of the continuous-spin representations admitted by \(ISO(2)\). We will compare the competing classical and quantum corrections to the leading classical eikonal scattering in the transplanckian regime and discuss how observables are extracted from the scattering phase matrix.
I will discuss the eikonal scattering of two gravitationally interacting bodies, showing that exponentiation of the scattering phase matrix is a direct consequence of the group contraction \(SU(2) \rightarrow ISO(2)\), in the large angular momentum limit. The emergence of the classical limit is understood in terms of the continuous-spin representations admitted by \(ISO(2)\). We will compare the competing classical and quantum corrections to the leading classical eikonal scattering in the transplanckian regime and discuss how observables are extracted from the scattering phase matrix.
Posted by: andrea
Tue
6 Jun 2023
TBA
Jorge Santos
(Cambridge University, DAMTP)
Abstract:
TBA
TBA
Posted by: IC
Tue
6 Jun 2023
Blackhole, Blackring transition
๐ London
Indranil Halder
(Harvard)
Abstract:
We will discuss BPS objects in M theory compactified on a Calabi-Yau three fold X. From the microscopic point of view such degeneracies are encoded in the partition function of the topological strings on X through the Gopakumar-Vafa formula. For the first part of the talk, as an example we will focus on quintic, and discuss how Gopakumar-Vafa invariants can be calculated systematically from the knowledge of boundary condition on the moduli space together with holomorphic ambiguity equation and mirror symmetry. When the entropy thus obtained is plotted against the left moving angular momentum for fixed M2 brane charge, there is a clear transition point at a critical angular momentum. Comparison of the the curve with leading order results from supergravity in 5d shows a large deviation. We will explain the conceptual origin of such deviations using Ooguri-Strominger-Vafa conjecture in 4d string theory though 4d-5d lift. In particular we will observe that the curve is well approximated by the (suitably corrected) entropy of BMPV blackhole for smaller angular momentum and for larger angular momentum by the (suitably corrected) entropy of a particular EEMR blackring. We will show that these observations remain valid on a class of one parameter Calabi-Yau three folds.
We will discuss BPS objects in M theory compactified on a Calabi-Yau three fold X. From the microscopic point of view such degeneracies are encoded in the partition function of the topological strings on X through the Gopakumar-Vafa formula. For the first part of the talk, as an example we will focus on quintic, and discuss how Gopakumar-Vafa invariants can be calculated systematically from the knowledge of boundary condition on the moduli space together with holomorphic ambiguity equation and mirror symmetry. When the entropy thus obtained is plotted against the left moving angular momentum for fixed M2 brane charge, there is a clear transition point at a critical angular momentum. Comparison of the the curve with leading order results from supergravity in 5d shows a large deviation. We will explain the conceptual origin of such deviations using Ooguri-Strominger-Vafa conjecture in 4d string theory though 4d-5d lift. In particular we will observe that the curve is well approximated by the (suitably corrected) entropy of BMPV blackhole for smaller angular momentum and for larger angular momentum by the (suitably corrected) entropy of a particular EEMR blackring. We will show that these observations remain valid on a class of one parameter Calabi-Yau three folds.
Posted by: andrea
Thu
1 Jun 2023
Hardy Lecture + Workshop
Eva Miranda
(Barcelona)
Abstract:
The London Institute hosts a workshop on the Navier-Stokes millennium-prize problem and its connection to fluid computing and machine learning.
https://lims.ac.uk/event/navier-stokes-regularity-fluid-computing-machine-learning-workshop/
https://www.lms.ac.uk/events/lectures/hardy-lectureship#LMS%20Hardy%20Lectureship
The London Institute hosts a workshop on the Navier-Stokes millennium-prize problem and its connection to fluid computing and machine learning.
https://lims.ac.uk/event/navier-stokes-regularity-fluid-computing-machine-learning-workshop/
https://www.lms.ac.uk/events/lectures/hardy-lectureship#LMS%20Hardy%20Lectureship
Posted by: oxford
May 2023
Wed
31 May 2023
Triangle Seminar - Entanglement and Emergent Space from Large Matrices
Sean Hartnoll
(University of Cambridge)
Abstract:
The locality in space of interactions between elementary particles is a key property of our universe. This locality is hardwired into quantum field theoretic descriptions of nature. However, locality and indeed space itself are likely not fundamental concepts. In holographic duality, local interactions on a dynamical spacetime emerge from "large N" matrices where no locality need be manifest in the microscopic Hamiltonian. The emergence of locality from matrix theories is well-established but not well-understood. In recent years it has been appreciated that locally is closely tied up with so-called "area law" entanglement of the microscopic degrees of freedom. I will discuss a particularly robust notion of entanglement in matrix theories that is rooted in an underlying Gauss law constraint and show how simple models of matrix, or 'fuzzy' geometry contain area law entanglement.
The locality in space of interactions between elementary particles is a key property of our universe. This locality is hardwired into quantum field theoretic descriptions of nature. However, locality and indeed space itself are likely not fundamental concepts. In holographic duality, local interactions on a dynamical spacetime emerge from "large N" matrices where no locality need be manifest in the microscopic Hamiltonian. The emergence of locality from matrix theories is well-established but not well-understood. In recent years it has been appreciated that locally is closely tied up with so-called "area law" entanglement of the microscopic degrees of freedom. I will discuss a particularly robust notion of entanglement in matrix theories that is rooted in an underlying Gauss law constraint and show how simple models of matrix, or 'fuzzy' geometry contain area law entanglement.
Posted by: IC2
Wed
31 May 2023
Triangle Seminar - Generalized Charges of Symmetries
Lakshya Bhardwaj
(University of Oxford)
Abstract:
I will describe how non-invertible global symmetries act on operators in a quantum field theory. The various possible actions are called generalized charges. This provides a stepping stone for understanding physical applications of non-invertible symmetries, as will be exemplified in the case of Ising symmetry. One of the surprising findings of this endeavor is that there exist new and unexplored generalized charges already for ordinary invertible global symmetries! These generalized charges are described by higher-representations of the symmetry group, generalizing the ordinary charges described by ordinary representations of the symmetry group.
I will describe how non-invertible global symmetries act on operators in a quantum field theory. The various possible actions are called generalized charges. This provides a stepping stone for understanding physical applications of non-invertible symmetries, as will be exemplified in the case of Ising symmetry. One of the surprising findings of this endeavor is that there exist new and unexplored generalized charges already for ordinary invertible global symmetries! These generalized charges are described by higher-representations of the symmetry group, generalizing the ordinary charges described by ordinary representations of the symmetry group.
Posted by: IC2
Tue
30 May 2023
CPT symmetry, analyticity and conformal symmetry: connecting particle physics to LCDM cosmology
Neil Turok
(University of Edinburgh and Perimeter Institute)
Abstract:
The universe has turned out to be simpler than expected on small and large scales. This encourages us to build unified theories connecting particle physics to the LCDM model. Instead of postulating an ``attractorรขโฌย phase such as inflation, prior to the hot big bang, we extrapolate the observed universe all the way back to the initial singularity. If the hot plasma in the early universe is perfectly conformal radiation, the singularity is only conformal and one can analytically extend cosmic spacetime and matter through it into a ``mirrorรขโฌย universe on the other side. The universe is then CPT symmetric. We calculate the gravitational entropy for cosmologies with radiation, matter, Lambda and space curvature, finding that thermodynamics favours flat, homogeneous and isotropic universes like ours. To maintain conformal symmetry we include unusual Dim-0 (dimension zero) fields, whose unique physical state is the vacuum. They improve the Standard Modelรขโฌโขs (SMรขโฌโขs) coupling to gravity, by cancelling the SMรขโฌโขs vacuum energy and two local รขโฌลWeylรขโฌย anomalies due to gauge fields and fermions. They also cancel the acausal, nonanalytic behaviour introduced into the graviton propagator by loops of SM particles. Cancellation requires (and predicts) precisely 3 generations of SM fermions, each with a RH neutrino, and that the Higgs is composite. One of the RH neutrinos, if stable, is then the simplest-yet proposed viable candidate for the dark matter. Galaxy surveys including EUCLID and LSST will allow precise tests soon. Finally, and most exciting, Dim-0 fields have scale-invariant fluctuations in the vacuum. These source curvature perturbations in the early universe. We recently calculated their power spectrum, ab initio, in terms of Standard Model couplings at the Planck scale. Subject to some theoretical assumptions, the amplitude and spectral tilt closely match the observations, with no free parameters. (See arXiv:2302.00344and references therein).
The universe has turned out to be simpler than expected on small and large scales. This encourages us to build unified theories connecting particle physics to the LCDM model. Instead of postulating an ``attractorรขโฌย phase such as inflation, prior to the hot big bang, we extrapolate the observed universe all the way back to the initial singularity. If the hot plasma in the early universe is perfectly conformal radiation, the singularity is only conformal and one can analytically extend cosmic spacetime and matter through it into a ``mirrorรขโฌย universe on the other side. The universe is then CPT symmetric. We calculate the gravitational entropy for cosmologies with radiation, matter, Lambda and space curvature, finding that thermodynamics favours flat, homogeneous and isotropic universes like ours. To maintain conformal symmetry we include unusual Dim-0 (dimension zero) fields, whose unique physical state is the vacuum. They improve the Standard Modelรขโฌโขs (SMรขโฌโขs) coupling to gravity, by cancelling the SMรขโฌโขs vacuum energy and two local รขโฌลWeylรขโฌย anomalies due to gauge fields and fermions. They also cancel the acausal, nonanalytic behaviour introduced into the graviton propagator by loops of SM particles. Cancellation requires (and predicts) precisely 3 generations of SM fermions, each with a RH neutrino, and that the Higgs is composite. One of the RH neutrinos, if stable, is then the simplest-yet proposed viable candidate for the dark matter. Galaxy surveys including EUCLID and LSST will allow precise tests soon. Finally, and most exciting, Dim-0 fields have scale-invariant fluctuations in the vacuum. These source curvature perturbations in the early universe. We recently calculated their power spectrum, ab initio, in terms of Standard Model couplings at the Planck scale. Subject to some theoretical assumptions, the amplitude and spectral tilt closely match the observations, with no free parameters. (See arXiv:2302.00344and references therein).
Posted by: IC
Tue
30 May 2023
Gluon scattering in AdS at finite string coupling
๐ London
Shai Chester
(Harvard)
Abstract:
We consider gluons scattering in Type IIB string theory on AdS5 x S^5/Z2 in the presence of D7 branes, which is dual to the flavor multiplet correlator in a certain 4d N=2 USp(2N) gauge theory with SO(8) flavor symmetry. We compute this holographic correlator in the large N and finite string coupling tau expansion using constraints from derivatives of the mass deformed sphere free energy, which we compute to all orders in 1/N and finite tau using localization. In particular, we fix the F^4 correction to gluon scattering on AdS in terms of Jacobi theta functions, and the D^2F^4 correction in terms of a non-holomorphic Eisenstein series. At weak string coupling, we find that the AdS correlator takes a remarkably similar form as the flat space Veneziano amplitude. Finally, we combine the numerical conformal bootstrap with the localization constraints to study the correlator at finite N and tau.
We consider gluons scattering in Type IIB string theory on AdS5 x S^5/Z2 in the presence of D7 branes, which is dual to the flavor multiplet correlator in a certain 4d N=2 USp(2N) gauge theory with SO(8) flavor symmetry. We compute this holographic correlator in the large N and finite string coupling tau expansion using constraints from derivatives of the mass deformed sphere free energy, which we compute to all orders in 1/N and finite tau using localization. In particular, we fix the F^4 correction to gluon scattering on AdS in terms of Jacobi theta functions, and the D^2F^4 correction in terms of a non-holomorphic Eisenstein series. At weak string coupling, we find that the AdS correlator takes a remarkably similar form as the flat space Veneziano amplitude. Finally, we combine the numerical conformal bootstrap with the localization constraints to study the correlator at finite N and tau.
Posted by: QMW
Wed
24 May 2023
Machine Learning and Flows for Lattice QCD
๐ London
Sebastien Racaniere
(Deepmind)
Abstract:
Recently, there have been some very impressive advances in generative models for sound, text and images. In this talk, I will look into applications of generative models to Lattice QCD. The models I will consider are flows, which are families of diffeomorphisms transforming simple base distributions into complicated target distributions. Traditional ML flows are on vector spaces, which is different from our setup where we need to deal with products of SU(N). I will give details on how we built these flows, and explain how known symmetries of LQCD can be incorporated into them.
Recently, there have been some very impressive advances in generative models for sound, text and images. In this talk, I will look into applications of generative models to Lattice QCD. The models I will consider are flows, which are families of diffeomorphisms transforming simple base distributions into complicated target distributions. Traditional ML flows are on vector spaces, which is different from our setup where we need to deal with products of SU(N). I will give details on how we built these flows, and explain how known symmetries of LQCD can be incorporated into them.
Posted by: andrea
Wed
24 May 2023
Integrated correlators in N=4 super Yang-Mills
Congkao Wen
(Queen Mary University of London)
Abstract:
Over the past few years, it has been shown that, when integrating out the spacetime dependence with a certain integration measure, some four-point correlation functions in N=4 super Yang-Mills (SYM) can be computed exactly. These physical observables are often called integrated correlators, which are functions of Yang-Mills coupling \tau, and transform under S-duality of N=4 SYM. In this talk, I will review some of the recent developments regarding these integrated correlators. In particular, I will discuss the so-called Laplace-difference equations that determine the integrated correlators recursively. I will also present the generating functions of the integrated correlators that resum the ranks of the gauge group and the charges of the operators, from which we will further determine the large-N and large-charge properties of the integrated correctors.
Over the past few years, it has been shown that, when integrating out the spacetime dependence with a certain integration measure, some four-point correlation functions in N=4 super Yang-Mills (SYM) can be computed exactly. These physical observables are often called integrated correlators, which are functions of Yang-Mills coupling \tau, and transform under S-duality of N=4 SYM. In this talk, I will review some of the recent developments regarding these integrated correlators. In particular, I will discuss the so-called Laplace-difference equations that determine the integrated correlators recursively. I will also present the generating functions of the integrated correlators that resum the ranks of the gauge group and the charges of the operators, from which we will further determine the large-N and large-charge properties of the integrated correctors.
Posted by: IC2
Tue
23 May 2023
Interacting UV fixed points in QFT and quantum gravity
Daniel Litim
(University of Sussex)
Abstract:
Free or interacting UV fixed points play a key role
in the fundamental definition of QFT. In this talk,
I give a broad overview of weakly and strongly interacting
fixed points in 3d and 4d QFTs including models of particle
physics with or without supersymmetry, and fermionic
theories. Further, I explain methods and ideas to search
for fixed points in 4d quantum gravity. Implications from
the viewpoint of CFTs and higher-spin gauge theories through
the AdS/CFT conjecture are also discussed.
Free or interacting UV fixed points play a key role
in the fundamental definition of QFT. In this talk,
I give a broad overview of weakly and strongly interacting
fixed points in 3d and 4d QFTs including models of particle
physics with or without supersymmetry, and fermionic
theories. Further, I explain methods and ideas to search
for fixed points in 4d quantum gravity. Implications from
the viewpoint of CFTs and higher-spin gauge theories through
the AdS/CFT conjecture are also discussed.
Posted by: IC
Mon
22 May 2023
LonTI: Leverhulme Lectures on Supersymmetry, complex geometry and the hyperkahler quotient
Ulf Lindstrom
(Uppsala)
Abstract:
Sigma models are maps from a domain to a target space T. The geometry of the target space is determined by the dimension of the domain and symmetries of the model. When it has isometries that can be gauged, the quotient space, i.e., the space of orbits under the isometries, supports a new sigma model. The target space geometry of the new model is the quotient of the T by the isometry group. This is first described for a bosonic sigma model and it is pointed out that we need to understand supersymmetric sigma models, their isometries and gauging as well as the quotient in order to apply the scheme to models with extended supersymmetry. We then look at these issues. The final goal is to construct new hyperkahler geometries from hyperkรยคhler geometries with isometries, so making sure that the quotient construction preserves the symmetries etc. Ulf Lindstrom is Leverhulme Visiting Professor at Imperial College.
Sigma models are maps from a domain to a target space T. The geometry of the target space is determined by the dimension of the domain and symmetries of the model. When it has isometries that can be gauged, the quotient space, i.e., the space of orbits under the isometries, supports a new sigma model. The target space geometry of the new model is the quotient of the T by the isometry group. This is first described for a bosonic sigma model and it is pointed out that we need to understand supersymmetric sigma models, their isometries and gauging as well as the quotient in order to apply the scheme to models with extended supersymmetry. We then look at these issues. The final goal is to construct new hyperkahler geometries from hyperkรยคhler geometries with isometries, so making sure that the quotient construction preserves the symmetries etc. Ulf Lindstrom is Leverhulme Visiting Professor at Imperial College.
Posted by: CityU2
Thu
18 May 2023
Higgs Workshop: Multiple scales and phase transitions in Large-N expansions and 2d gravity
๐ London
Ines Aniceto
(Southampton)
Abstract:
Matrix models offer non-perturbative descriptions of quantum gravity in simple settings, allowing us to study large-N dualities between gauge and string theories. However, the large-N expansions of matrix models lead to divergent series, only defined as asymptotic series. By fine-tuning the couplings of the matrix model we obtain models of pure gravity coupled to minimal conformal field theories. The free energy for the simplest of these "minimal models" is 2d gravity also admits an asymptotic expansion which formally satisfies the Painlevรยฉ I equation.
These asymptotic properties are connected to the existence of exponentially small contributions not captured by a perturbative analysis and whose physical interpretation can be elusive. The emerging structure can be accurately described by means of a resurgent transseries, capturing this perturbative/non-perturbative connection and its consequences. This talk will focus on the essential role of this resurgent transseries for the cases of Painlevรยฉ I and the quartic matrix model: together with exponentially accurate numerical and summation methods, one can show how to go beyond the asymptotic results and obtain (analytically and numerically) non-perturbative data.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
Matrix models offer non-perturbative descriptions of quantum gravity in simple settings, allowing us to study large-N dualities between gauge and string theories. However, the large-N expansions of matrix models lead to divergent series, only defined as asymptotic series. By fine-tuning the couplings of the matrix model we obtain models of pure gravity coupled to minimal conformal field theories. The free energy for the simplest of these "minimal models" is 2d gravity also admits an asymptotic expansion which formally satisfies the Painlevรยฉ I equation.
These asymptotic properties are connected to the existence of exponentially small contributions not captured by a perturbative analysis and whose physical interpretation can be elusive. The emerging structure can be accurately described by means of a resurgent transseries, capturing this perturbative/non-perturbative connection and its consequences. This talk will focus on the essential role of this resurgent transseries for the cases of Painlevรยฉ I and the quartic matrix model: together with exponentially accurate numerical and summation methods, one can show how to go beyond the asymptotic results and obtain (analytically and numerically) non-perturbative data.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
Posted by: andrea
Thu
18 May 2023
Higgs Workshop: Kinetic Theory of Waves for Turbulent States
๐ London
Vladimir Rosenhaus
(CUNY, Graduate Center)
Abstract:
For a weakly nonlinear classical system, the kinetic equation for waves governs the evolution of the occupation number of a given wavevector. It is like the Boltzmann equation, but for waves instead of particles. As has been known for half a century, in addition to thermal equilibrium, the kinetic equation has another stationary solution: a turbulent state, describing a cascade of energy. Wave turbulence is observed in a wide range of physical contexts, most notably in surface gravity waves in the ocean. Higher order terms in the kinetic equation, going beyond leading order in the nonlinearity, have never been computed. We describe a method, based on quantum field theory, for computing such terms. We show that higher order terms can exhibit UV divergences. We sum the most divergent diagrams (bubble diagrams) to derive a kind of renormalized kinetic equation. Based on 2203.08168, 2212.02555, and work in progress with G. Falkovich.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
For a weakly nonlinear classical system, the kinetic equation for waves governs the evolution of the occupation number of a given wavevector. It is like the Boltzmann equation, but for waves instead of particles. As has been known for half a century, in addition to thermal equilibrium, the kinetic equation has another stationary solution: a turbulent state, describing a cascade of energy. Wave turbulence is observed in a wide range of physical contexts, most notably in surface gravity waves in the ocean. Higher order terms in the kinetic equation, going beyond leading order in the nonlinearity, have never been computed. We describe a method, based on quantum field theory, for computing such terms. We show that higher order terms can exhibit UV divergences. We sum the most divergent diagrams (bubble diagrams) to derive a kind of renormalized kinetic equation. Based on 2203.08168, 2212.02555, and work in progress with G. Falkovich.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
Posted by: andrea
Thu
18 May 2023
Higgs Workshop: Radiation from Matrices
๐ London
Bartomeu Fiol
(Barcelona)
Abstract:
I give an overview of work characterizing radiation in generic four-dimensional conformal field theories. I argue that for theories with conformal scalars, the radiated energy is not positive definite and the radiated power is not Lorentz invariant. I then determine the coupling dependence of radiation, for N=2 superconformal field theories in the planar limit. This involves a purely combinatorial solution of certain matrix models, in terms of tree graphs.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
I give an overview of work characterizing radiation in generic four-dimensional conformal field theories. I argue that for theories with conformal scalars, the radiated energy is not positive definite and the radiated power is not Lorentz invariant. I then determine the coupling dependence of radiation, for N=2 superconformal field theories in the planar limit. This involves a purely combinatorial solution of certain matrix models, in terms of tree graphs.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
Posted by: oxford
Wed
17 May 2023
Higgs Workshop: Black holes and other phases of super Yang-Mills from matrices
๐ London
Sameer Murthy
(King's)
Abstract:
The superconformal index of N=4 super Yang-Mills theory on a three-sphere is captured by a unitary matrix model with purely double trace operators in the action. The AdS/CFT correspondence predicts that this index should have exponential growth at large charges and large N, corresponding to the 1/16-BPS black hole (BH) in AdS5. I will show how the matrix model gives rise to this expected BH growth as well as an infinite number of new phases. In particular, I will introduce a deformation of the matrix model which allows us to solve it at large N. The deformation has interesting relations with the Bloch-Wigner dilogarithm, a function introduced by number theorists.
I will then show how this matrix model can be expressed in terms of a system of free fermions in a certain ensemble. Integrating out the fermions and averaging over the ensemble leads to a convergent expansion as a series of determinants, showing how giant gravitons in the dual AdS5 are encoded in the gauge theory.
.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
The superconformal index of N=4 super Yang-Mills theory on a three-sphere is captured by a unitary matrix model with purely double trace operators in the action. The AdS/CFT correspondence predicts that this index should have exponential growth at large charges and large N, corresponding to the 1/16-BPS black hole (BH) in AdS5. I will show how the matrix model gives rise to this expected BH growth as well as an infinite number of new phases. In particular, I will introduce a deformation of the matrix model which allows us to solve it at large N. The deformation has interesting relations with the Bloch-Wigner dilogarithm, a function introduced by number theorists.
I will then show how this matrix model can be expressed in terms of a system of free fermions in a certain ensemble. Integrating out the fermions and averaging over the ensemble leads to a convergent expansion as a series of determinants, showing how giant gravitons in the dual AdS5 are encoded in the gauge theory.
.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
Posted by: andrea
Wed
17 May 2023
Higgs Workshop: Emergent Ensemble Symmetries in Holography
๐ London
Jacob Leedom
(DESY)
Abstract:
Dualities involving ensembles of theories represent a fascinating class of holographic correspondences. The inclusion of wormholes into a theory naturally motivates the study of ensembles, but doing so leads to many puzzles from the viewpoint of string theory. In this talk, I will discuss holographic dualities involving ensembles of 2D Narain conformal field theories. The bulk dual of such an ensemble is an Abelian Chern-Simons theory, but features a sum over 3D geometries. Generalizations of this correspondence lead to emergent ensemble symmetries รขโฌโ global symmetries that appear after averaging over the ensemble and are the vestiges of T-duality in the CFT. These symmetries are intimately related to the anyon data and 0-form symmetries of the bulk Chern-Simons theories. I will also discuss the relation of these emergent global symmetries with recent ideas in quantum gravity, and furthermore generally discuss the role of ensemble averaging in standard holography, the landscape, and the swampland.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
Dualities involving ensembles of theories represent a fascinating class of holographic correspondences. The inclusion of wormholes into a theory naturally motivates the study of ensembles, but doing so leads to many puzzles from the viewpoint of string theory. In this talk, I will discuss holographic dualities involving ensembles of 2D Narain conformal field theories. The bulk dual of such an ensemble is an Abelian Chern-Simons theory, but features a sum over 3D geometries. Generalizations of this correspondence lead to emergent ensemble symmetries รขโฌโ global symmetries that appear after averaging over the ensemble and are the vestiges of T-duality in the CFT. These symmetries are intimately related to the anyon data and 0-form symmetries of the bulk Chern-Simons theories. I will also discuss the relation of these emergent global symmetries with recent ideas in quantum gravity, and furthermore generally discuss the role of ensemble averaging in standard holography, the landscape, and the swampland.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
Posted by: andrea
Wed
17 May 2023
On Quantum Transitions, Detailed Balance and Nothingness
Fernando Quevedo
(University of Cambridge)
Abstract:
We consider vacuum transitions by bubble nucleation among vacua with different values and signs of the cosmological constant Lambda, including both up and down tunnelings. Following the Hamiltonian formalism in four dimensions, we explicitly compute the decay rates for all possible combinations of initial and final values of Lambda and find that up-tunneling may be allowed starting not only from pure dS spacetime but also from pure AdS and Minkowski spacetimes. We trace the difference with the Euclidean approach, for which these transitions are found not to be allowed, to the difference of assigning either vanishing or infinite entropy to both pure AdS and Minkowski. We find that, in all allowed cases, detailed balance is satisfied. Also in the formal limit Lambda -> -infinity, the transition rates for AdS to dS agree with the Hartle-Hawking and Vilenkin amplitudes for the creation of dS from nothing. This is consistent with a proposal of Brown and Dahlen to define 'nothing' as AdS in this limit. We generalise our results to include black hole backgrounds for which transitions are allowed only in certain regimes of the black hole mass M but detailed balance is not satisfied, except for Schwarzschild de Sitter (SdS) to another SdS for which the transition is allowed and detailed balance satisfied. We compute the bubble trajectory after nucleation and find that, contrary to the M = 0 case, the trajectory is not a geodesic for the open universe slicing of dS. We briefly discuss the relevance of our results to the string landscape.
We consider vacuum transitions by bubble nucleation among vacua with different values and signs of the cosmological constant Lambda, including both up and down tunnelings. Following the Hamiltonian formalism in four dimensions, we explicitly compute the decay rates for all possible combinations of initial and final values of Lambda and find that up-tunneling may be allowed starting not only from pure dS spacetime but also from pure AdS and Minkowski spacetimes. We trace the difference with the Euclidean approach, for which these transitions are found not to be allowed, to the difference of assigning either vanishing or infinite entropy to both pure AdS and Minkowski. We find that, in all allowed cases, detailed balance is satisfied. Also in the formal limit Lambda -> -infinity, the transition rates for AdS to dS agree with the Hartle-Hawking and Vilenkin amplitudes for the creation of dS from nothing. This is consistent with a proposal of Brown and Dahlen to define 'nothing' as AdS in this limit. We generalise our results to include black hole backgrounds for which transitions are allowed only in certain regimes of the black hole mass M but detailed balance is not satisfied, except for Schwarzschild de Sitter (SdS) to another SdS for which the transition is allowed and detailed balance satisfied. We compute the bubble trajectory after nucleation and find that, contrary to the M = 0 case, the trajectory is not a geodesic for the open universe slicing of dS. We briefly discuss the relevance of our results to the string landscape.
Posted by: IC2
Wed
17 May 2023
Higgs Workshop: TBA
๐ London
Miguel Paulos
(ENS, Paris)
Abstract:
TBA.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
TBA.
If you are planning to attend, please send and email to pietro.benetti_genolini@kcl.ac.uk or alan.rios_fukelman@kcl.ac.uk so your name is added to the participants list in order to grant you access to the building.
Posted by: andrea
Tue
16 May 2023
TBA
Marco Scalisi
(Max Planck Institute)
Mon
15 May 2023
LonTI: Leverhulme Lectures on Supersymmetry, complex geometry and the hyperkahler quotient
Ulf Lindstrom
(Uppsala)
Abstract:
Sigma models are maps from a domain to a target space T. The geometry of the target space is determined by the dimension of the domain and symmetries of the model. When it has isometries that can be gauged, the quotient space, i.e., the space of orbits under the isometries, supports a new sigma model. The target space geometry of the new model is the quotient of the T by the isometry group.
This is first described for a bosonic sigma model and it is pointed out that we need to understand supersymmetric sigma models, their isometries and gauging as well as the quotient in order to apply the scheme to models with extended supersymmetry. We then look at these issues. The final goal is to construct new hyperkahler geometries from hyperkรยคhler geometries with isometries, so making sure that the quotient construction preserves the symmetries etc.
Ulf Lindstrom is Leverhulme Visiting Professor at Imperial College.
Sigma models are maps from a domain to a target space T. The geometry of the target space is determined by the dimension of the domain and symmetries of the model. When it has isometries that can be gauged, the quotient space, i.e., the space of orbits under the isometries, supports a new sigma model. The target space geometry of the new model is the quotient of the T by the isometry group.
This is first described for a bosonic sigma model and it is pointed out that we need to understand supersymmetric sigma models, their isometries and gauging as well as the quotient in order to apply the scheme to models with extended supersymmetry. We then look at these issues. The final goal is to construct new hyperkahler geometries from hyperkรยคhler geometries with isometries, so making sure that the quotient construction preserves the symmetries etc.
Ulf Lindstrom is Leverhulme Visiting Professor at Imperial College.
Posted by: CityU2
Mon
15 May 2023
Holographic description of code CFTs
๐ London
Anatoly Dymarsky
(Kentucky)
Abstract:
Recently, a relation was introduced connecting codes of various types with the space of abelian (Narain) 2d CFTs. We extend this relation to provide holographic description of code CFTs in terms of abelian Chern-Simons theory in the bulk. For codes over the alphabet Z_p corresponding bulk theory is, schematically, U(1)_p times U(1)_{-p} where p stands for the level. Furthermore, CFT partition function averaged over all code theories for the codes of a given type is holographically given by the Chern-Simons partition function summed over all possible 3d geometries. This provides an explicit and controllable example of holographic correspondence where a finite ensemble of CFTs is dual to "topological/CS gravity" in the bulk. The parameter p controls the size of the ensemble and "how topological" the bulk theory is. Say, for p=1 any given Narain CFT is described holographically in terms of U(1)_1^n times U(1)_{-1}^n Chern-Simons, which does not distinguish between different 3d geometries (and hence can be evaluated on any of them). When p approaches infinity, the ensemble of code theories covers the whole Narain moduli space with the bulk theory becoming "U(1)-gravity" proposed by Maloney-Witten and Afkhami-Jeddi et al.
Recently, a relation was introduced connecting codes of various types with the space of abelian (Narain) 2d CFTs. We extend this relation to provide holographic description of code CFTs in terms of abelian Chern-Simons theory in the bulk. For codes over the alphabet Z_p corresponding bulk theory is, schematically, U(1)_p times U(1)_{-p} where p stands for the level. Furthermore, CFT partition function averaged over all code theories for the codes of a given type is holographically given by the Chern-Simons partition function summed over all possible 3d geometries. This provides an explicit and controllable example of holographic correspondence where a finite ensemble of CFTs is dual to "topological/CS gravity" in the bulk. The parameter p controls the size of the ensemble and "how topological" the bulk theory is. Say, for p=1 any given Narain CFT is described holographically in terms of U(1)_1^n times U(1)_{-1}^n Chern-Simons, which does not distinguish between different 3d geometries (and hence can be evaluated on any of them). When p approaches infinity, the ensemble of code theories covers the whole Narain moduli space with the bulk theory becoming "U(1)-gravity" proposed by Maloney-Witten and Afkhami-Jeddi et al.
Posted by: andrea
Wed
10 May 2023
Localizing information in quantum gravity
๐ London
Alex Belin
(Milano Bicocca)
Abstract:
Locality is a powerful property of quantum field theory and implies that information can be strictly localized in regions of space, and is completely inaccessible from far away. On the other hand, the holographic nature of quantum gravity suggests that the theory is ultimately non-local and that information can never be localized deep inside some spacetime region, but rather is always accessible from the boundary. This is meant to hold as a non-perturbative statement and it remains to be understood whether quantum information can be localized within G_N perturbation theory. In this talk, I will address this problem from the point of view of the AdS/CFT correspondence. I will construct candidate local operators that can be used to localize information deep inside the bulk. They have the following two properties: they act just like standard HKLL operators to leading order at large N, but commute with the CFT Hamiltonian to all orders in 1/N. These operators can only be constructed in a particular class of states which have a large energy variance, for example coherent states corresponding to semi-classical geometries. The interpretation of these operators is that they are dressed with respect to a feature of the state, rather than to the boundary.
Locality is a powerful property of quantum field theory and implies that information can be strictly localized in regions of space, and is completely inaccessible from far away. On the other hand, the holographic nature of quantum gravity suggests that the theory is ultimately non-local and that information can never be localized deep inside some spacetime region, but rather is always accessible from the boundary. This is meant to hold as a non-perturbative statement and it remains to be understood whether quantum information can be localized within G_N perturbation theory. In this talk, I will address this problem from the point of view of the AdS/CFT correspondence. I will construct candidate local operators that can be used to localize information deep inside the bulk. They have the following two properties: they act just like standard HKLL operators to leading order at large N, but commute with the CFT Hamiltonian to all orders in 1/N. These operators can only be constructed in a particular class of states which have a large energy variance, for example coherent states corresponding to semi-classical geometries. The interpretation of these operators is that they are dressed with respect to a feature of the state, rather than to the boundary.
Posted by: andrea
Wed
10 May 2023
Exploring Low-Dimensional Quantum Spectral Curves
Simon Ekhammar
(Uppsala U., Sweden)
Abstract:
The Quantum Spectral Curve (QSC) is a powerful integrability-based formalism capable of computing the non-perturbative spectrum of planar N=4 SYM. The success and utility of QSC motivate trying to extend it beyond N=4 to other instances of the AdS/CFT correspondence where integrability is expected to be present. This has been successfully accomplished for AdS4/CFT3 and a curve has been conjectured for AdS3/CFT2.
I will review the basics of the QSC framework in the well-understood AdS5 case and then turn to low-dimensional versions of the QSC. I will discuss the conjectured curve for AdS3 and how it differs from previous iterations of the QSC. Furthermore, I will discuss recent perturbative results with a peculiar structure.
The Quantum Spectral Curve (QSC) is a powerful integrability-based formalism capable of computing the non-perturbative spectrum of planar N=4 SYM. The success and utility of QSC motivate trying to extend it beyond N=4 to other instances of the AdS/CFT correspondence where integrability is expected to be present. This has been successfully accomplished for AdS4/CFT3 and a curve has been conjectured for AdS3/CFT2.
I will review the basics of the QSC framework in the well-understood AdS5 case and then turn to low-dimensional versions of the QSC. I will discuss the conjectured curve for AdS3 and how it differs from previous iterations of the QSC. Furthermore, I will discuss recent perturbative results with a peculiar structure.
Posted by: IC2
Mon
8 May 2023
TBA
๐ London
Nima Lashkari
(Purdue)
Sun
7 May 2023
Theory Colloquium - Hide and seek: how new physics can hide in the proton
Maria Ubiali
(DAMPT)
Abstract:
The interpretation of LHC data, and the assessment of possible hints for new physics in the experimental signals, require the precise knowledge of the proton subnuclear structure in terms of its elementary constituents, quarks and gluons.
In this talk I will present the fascinating precision frontier that phenomenologists are facing an will describe the challenges behind the determination of proton structure, involving precise perturbative QCD calculations and machine learning techniques. I will show how global fits of the proton might inadvertently รขโฌหfit awayรขโฌโข signals of new physics in the high-energy tails of the distributions that are experimentally measured. A new physics scenario in which the fit of the protonรขโฌโขs structure may completely absorb such signs of new physics is showcased.
Strategies to single out such effects and disentangle the inconsistencies that stem from new physics signals are discussed.
The interpretation of LHC data, and the assessment of possible hints for new physics in the experimental signals, require the precise knowledge of the proton subnuclear structure in terms of its elementary constituents, quarks and gluons.
In this talk I will present the fascinating precision frontier that phenomenologists are facing an will describe the challenges behind the determination of proton structure, involving precise perturbative QCD calculations and machine learning techniques. I will show how global fits of the proton might inadvertently รขโฌหfit awayรขโฌโข signals of new physics in the high-energy tails of the distributions that are experimentally measured. A new physics scenario in which the fit of the protonรขโฌโขs structure may completely absorb such signs of new physics is showcased.
Strategies to single out such effects and disentangle the inconsistencies that stem from new physics signals are discussed.
Posted by: IC2
Thu
4 May 2023
Self-dual gravity and color/kinematics duality in AdS4
๐ London
Silvia Nagy
(Durham)
Abstract:
I will show that self-dual gravity in Euclidean four-dimensional Anti-de Sitter space (AdS4 ) can be described by a minimally coupled scalar field with a cubic interaction written in terms of a deformed Poisson bracket, providing a remarkably simple generalisation of the Plebanski action for self-dual gravity in flat space. This implies a novel symmetry algebra in self-dual gravity, notably an AdS4 version of the so-called kinematic algebra. This provides a concrete starting point for defining the double copy for Einstein gravity in AdS4 by expanding around the self-dual sector. Moreover, I will show that the new kinematic Lie algebra can be lifted to a deformed version of the w1+รขหลพ algebra, which plays a prominent role in celestial holography.
I will show that self-dual gravity in Euclidean four-dimensional Anti-de Sitter space (AdS4 ) can be described by a minimally coupled scalar field with a cubic interaction written in terms of a deformed Poisson bracket, providing a remarkably simple generalisation of the Plebanski action for self-dual gravity in flat space. This implies a novel symmetry algebra in self-dual gravity, notably an AdS4 version of the so-called kinematic algebra. This provides a concrete starting point for defining the double copy for Einstein gravity in AdS4 by expanding around the self-dual sector. Moreover, I will show that the new kinematic Lie algebra can be lifted to a deformed version of the w1+รขหลพ algebra, which plays a prominent role in celestial holography.
Posted by: QMW
Wed
3 May 2023
Adventures in Flatland: Quantum Criticality in the 2+1d Thirring Model
๐ London
Simon Hands
(Liverpool)
Abstract:
The Thirring Model is a covariant quantum field theory of interacting fermions, sharing many features in common with
effective theories of two-dimensional electronic systems with linear dispersion such as graphene. For a small number of flavors and sufficiently strong interactions the ground state may be disrupted by condensation of particle-hole pairs leading to a quantum critical point. With no small dimensionless parameters in play in this regime the Thirring model is plausibly the simplest theory of fermions requiring a numerical solution. I will review what is currently known focussing on recent simulations employing Domain Wall Fermions (a formulation drawn from state-of-the-art QCD simulation), to faithfully capture the underlying symmetries at the critical point, focussing on the symmetry-breaking transition, the critical flavor number, and the anomalous scaling of the propagating fermion.
The Thirring Model is a covariant quantum field theory of interacting fermions, sharing many features in common with
effective theories of two-dimensional electronic systems with linear dispersion such as graphene. For a small number of flavors and sufficiently strong interactions the ground state may be disrupted by condensation of particle-hole pairs leading to a quantum critical point. With no small dimensionless parameters in play in this regime the Thirring model is plausibly the simplest theory of fermions requiring a numerical solution. I will review what is currently known focussing on recent simulations employing Domain Wall Fermions (a formulation drawn from state-of-the-art QCD simulation), to faithfully capture the underlying symmetries at the critical point, focussing on the symmetry-breaking transition, the critical flavor number, and the anomalous scaling of the propagating fermion.
Posted by: andrea
Wed
3 May 2023
Doubled space and extended supersymmetry
Ondrej Hulik
(Vrije U., Brussels)
Abstract:
In this talk I will discuss N=(2,2) susy generalisation of Hull's doubled sigma model. The doubled formulation of the worldsheet provides a description of string theory in which T-duality is promoted to a manifest symmetry. Formulation via N=(2,2) superspace provides a doubled formulation for bi-Hermitian/generalised Kahler target spaces. The theory is described by a single function, a doubled-generalised Kahler potential, supplemented with a manifestly N=(2,2) constraint. If time permits I will ilustrate some of the concepts developed on examples.
In this talk I will discuss N=(2,2) susy generalisation of Hull's doubled sigma model. The doubled formulation of the worldsheet provides a description of string theory in which T-duality is promoted to a manifest symmetry. Formulation via N=(2,2) superspace provides a doubled formulation for bi-Hermitian/generalised Kahler target spaces. The theory is described by a single function, a doubled-generalised Kahler potential, supplemented with a manifestly N=(2,2) constraint. If time permits I will ilustrate some of the concepts developed on examples.
Posted by: IC2
Tue
2 May 2023
LonTI: Introduction to Seiberg-Witten theory
Elli Pomoni
(DESY)
Abstract:
These three lectures will aim to provide a pedagogical introduction to the dynamics of N=2 supersymmetric gauge theory and the work of Seiberg and Witten. We will assume only basic knowledge of supersymmetry.
These three lectures will aim to provide a pedagogical introduction to the dynamics of N=2 supersymmetric gauge theory and the work of Seiberg and Witten. We will assume only basic knowledge of supersymmetry.
Posted by: CityU2
Tue
2 May 2023
Supersymmetric Massive Gravity
Laura Johnson
(Zurich, ETH)
Abstract:
In this talk, we start by introducing massive spin-2 theories and reviewing some of their key features. Then, using massive spinor helicity variables, we review an on-shell superspace formalism for massive particles in four dimensions. Finally, we apply this formalism to massive spin-2 amplitudes, deriving all spin-2 cubic vertices that are compatible with supersymmetry and exploring the constraints that adding more supersymmetry has on these vertices. Additionally, we discuss how the massive graviton supermultiplets and cubic superamplitudes can be constructed via a double copy of massive YangรขโฌโMills supermultiplets and cubic superamplitudes. We conclude by commenting on possible future directions such as computing the 4-point massive supersymmetric spin-2 amplitudes and the issues that can arise in a massive double copy for higher point amplitudes.
In this talk, we start by introducing massive spin-2 theories and reviewing some of their key features. Then, using massive spinor helicity variables, we review an on-shell superspace formalism for massive particles in four dimensions. Finally, we apply this formalism to massive spin-2 amplitudes, deriving all spin-2 cubic vertices that are compatible with supersymmetry and exploring the constraints that adding more supersymmetry has on these vertices. Additionally, we discuss how the massive graviton supermultiplets and cubic superamplitudes can be constructed via a double copy of massive YangรขโฌโMills supermultiplets and cubic superamplitudes. We conclude by commenting on possible future directions such as computing the 4-point massive supersymmetric spin-2 amplitudes and the issues that can arise in a massive double copy for higher point amplitudes.
Posted by: IC
Tue
2 May 2023
Small Bosonic CFTs, Chiral Fermionization, and Symmetry/Subalgebra Duality
๐ London
Brandon Rayhaun
(Simons Center for Geometry and Physics)
Abstract:
Conformal field theories in (1+1)D are key actors in many dramas in physics and mathematics. Their classification has therefore been an important and long-standing problem. In this talk, I will describe the main ideas behind the classification of (most) "small" bosonic CFTs - theories with low central charge (less than 24) and few primary operators (less than 5). I will then highlight two applications of this result. First, I will describe how it can be used in tandem with bosonization and fermionization techniques to establish the classification of chiral fermionic CFTs with central charge less than 23. Second, I will showcase how it can be used to bootstrap the generalized global symmetries of chiral bosonic CFTs.
Talk based on arXiv:2208.05486 [hep-th] (joint work with Sunil Mukhi) and arXiv:2303.16921 [hep-th].
Conformal field theories in (1+1)D are key actors in many dramas in physics and mathematics. Their classification has therefore been an important and long-standing problem. In this talk, I will describe the main ideas behind the classification of (most) "small" bosonic CFTs - theories with low central charge (less than 24) and few primary operators (less than 5). I will then highlight two applications of this result. First, I will describe how it can be used in tandem with bosonization and fermionization techniques to establish the classification of chiral fermionic CFTs with central charge less than 23. Second, I will showcase how it can be used to bootstrap the generalized global symmetries of chiral bosonic CFTs.
Talk based on arXiv:2208.05486 [hep-th] (joint work with Sunil Mukhi) and arXiv:2303.16921 [hep-th].
Posted by: QMW
April 2023
Thu
27 Apr 2023
LonTI: Introduction to Seiberg-Witten theory
Elli Pomoni
(DESY)
Abstract:
These three lectures will aim to provide a pedagogical introduction to the dynamics of N=2 supersymmetric gauge theory and the work of Seiberg and Witten. We will assume only basic knowledge of supersymmetry.
These three lectures will aim to provide a pedagogical introduction to the dynamics of N=2 supersymmetric gauge theory and the work of Seiberg and Witten. We will assume only basic knowledge of supersymmetry.
Posted by: CityU2
Wed
26 Apr 2023
Comments on factorisation in JT and 3d gravity
๐ London
Joan Simon Soler
(Edinburgh)
Abstract:
Using the BF formulation of JT gravity, we will extend the factorisation techniques in BF theory with compact groups to non-compact ones. The Euclidean path integral formulation of these theories provides some locality interpretation of these results in terms of gravitational edge modes. We shall comment on how to extend these ideas to 3d gravity. We will aim to stress differences occurring between gauge and gravity theories already in these low dimensional examples.
Using the BF formulation of JT gravity, we will extend the factorisation techniques in BF theory with compact groups to non-compact ones. The Euclidean path integral formulation of these theories provides some locality interpretation of these results in terms of gravitational edge modes. We shall comment on how to extend these ideas to 3d gravity. We will aim to stress differences occurring between gauge and gravity theories already in these low dimensional examples.
Posted by: andrea
Tue
25 Apr 2023
Generalised symmetries and dualities on the lattice
๐ London
Clement Delcamp
(Gent U)
Abstract:
Generalised notions of symmetries have received widespread attention in recent years. Though exotic, such generalised symmetries have been shown to naturally arise for instance as dual symmetries upon gauging ordinary symmetries. In this talk, I will present a systematic framework to investigate dualities of quantum lattice models and study the resulting generalised symmetries. I will illustrate this framework in the context of familiar spin models.
Generalised notions of symmetries have received widespread attention in recent years. Though exotic, such generalised symmetries have been shown to naturally arise for instance as dual symmetries upon gauging ordinary symmetries. In this talk, I will present a systematic framework to investigate dualities of quantum lattice models and study the resulting generalised symmetries. I will illustrate this framework in the context of familiar spin models.
Posted by: QMW
Mon
24 Apr 2023
LonTI: Introduction to Seiberg-Witten theory
Elli Pomoni
(DESY)
Abstract:
These three lectures will aim to provide a pedagogical introduction to the dynamics of N=2 supersymmetric gauge theory and the work of Seiberg and Witten. We will assume only basic knowledge of supersymmetry.
These three lectures will aim to provide a pedagogical introduction to the dynamics of N=2 supersymmetric gauge theory and the work of Seiberg and Witten. We will assume only basic knowledge of supersymmetry.
Posted by: CityU2
Thu
20 Apr 2023
Evanescent integrals from local subtraction
๐ London
Alessandro Georgoudis
(Nordita)
Abstract:
When computing scattering amplitudes in dimensional regularization, one frequently encounters contributions whose integrands vanish in strictly four dimensions. While these "evanescent" integrals can be handled with dimensional shift identities at one-loop, a similar treatment at the next perturbative order is insufficient. In this talk, we introduce a novel systematic method to compute evanescent contributions. By employing the local subtraction method of Anastasiou and Sterman we show that evanescent Feynman integrals are controlled by regions of loop-momentum space associated to ultra-violet, soft or collinear divergences. These integrals are then reduced to either products of one-loop integrals or one-fold integrals thereof. Starting from known integrands, we use this technique to easily recompute the leading-color two-loop four- and five-gluon QCD amplitudes in the all-plus helicity configuration. Remarkably, we find that the finite remainder is given by contributions arising from only ultra-violet regions of momentum space, and that the collinear contributions cancel in a highly non-trivial way.
When computing scattering amplitudes in dimensional regularization, one frequently encounters contributions whose integrands vanish in strictly four dimensions. While these "evanescent" integrals can be handled with dimensional shift identities at one-loop, a similar treatment at the next perturbative order is insufficient. In this talk, we introduce a novel systematic method to compute evanescent contributions. By employing the local subtraction method of Anastasiou and Sterman we show that evanescent Feynman integrals are controlled by regions of loop-momentum space associated to ultra-violet, soft or collinear divergences. These integrals are then reduced to either products of one-loop integrals or one-fold integrals thereof. Starting from known integrands, we use this technique to easily recompute the leading-color two-loop four- and five-gluon QCD amplitudes in the all-plus helicity configuration. Remarkably, we find that the finite remainder is given by contributions arising from only ultra-violet regions of momentum space, and that the collinear contributions cancel in a highly non-trivial way.
Posted by: QMW
Wed
19 Apr 2023
Line defects, rational Q-systems, and higher symmetries in 3d N=4 theories
Marcus Sperling
(Southeast U., Nanjing)
Abstract:
In this talk, I explore the set of line defects supported by 3D N=4 theories, and their significance in the context of generalised symmetries. I begin by discussing mirror symmetry of line defects using the example of Sp(k) SQCD and its two mirror theories. I then introduce rational Q-systems, a powerful technique borrowed from spin-chains/integrability, for evaluating twisted indices and studying line operator correlation functions. Finally, I highlight the role of line defects in realising mirror symmetry in the presence of non-trivial higher symmetries
In this talk, I explore the set of line defects supported by 3D N=4 theories, and their significance in the context of generalised symmetries. I begin by discussing mirror symmetry of line defects using the example of Sp(k) SQCD and its two mirror theories. I then introduce rational Q-systems, a powerful technique borrowed from spin-chains/integrability, for evaluating twisted indices and studying line operator correlation functions. Finally, I highlight the role of line defects in realising mirror symmetry in the presence of non-trivial higher symmetries
Posted by: IC2
Thu
13 Apr 2023
IR dualities across dimensions
๐ London
Shlomo Razamat
(Technion)
Abstract:
We will overview some of the recent progress regarding IR dualities across dimensions. In such dualities one engineers the same low energy QFT starting from high energy descriptions in different space-time dimensions. We will review how various strong coupling phenomena can follow from embedding the system of interest in such an across dimensions setup. We will also outline some of the open problems/questions in the field.
We will overview some of the recent progress regarding IR dualities across dimensions. In such dualities one engineers the same low energy QFT starting from high energy descriptions in different space-time dimensions. We will review how various strong coupling phenomena can follow from embedding the system of interest in such an across dimensions setup. We will also outline some of the open problems/questions in the field.
Posted by: QMW
Wed
12 Apr 2023
Lieb-Schultz-Mattis, t Hooft and Luttinger: anomalies in lattice systems
๐ London
Meng Cheng
(Yale)
Abstract:
In this talk I will discuss aspects of global symmetry and their t Hooft anomalies in lattice systems. I will discuss how anomalies are defined and probed using topological defects, which will be applied to both internal and lattice symmetries. The latter arise in systems satisfying Lieb-Schultz-Mattis-type theorems. Using the example of a spin-1/2 XXZ chain, I will also discuss how the continuum limit of a lattice model is properly described in terms of a low-energy theory with topological defects. In particular, I will show that t Hooft anomaly explains a curious size dependence of the ground state lattice momentum in the spin-1/2 XXZ chain.
In this talk I will discuss aspects of global symmetry and their t Hooft anomalies in lattice systems. I will discuss how anomalies are defined and probed using topological defects, which will be applied to both internal and lattice symmetries. The latter arise in systems satisfying Lieb-Schultz-Mattis-type theorems. Using the example of a spin-1/2 XXZ chain, I will also discuss how the continuum limit of a lattice model is properly described in terms of a low-energy theory with topological defects. In particular, I will show that t Hooft anomaly explains a curious size dependence of the ground state lattice momentum in the spin-1/2 XXZ chain.
Posted by: QMW
Wed
12 Apr 2023
String duals of two-dimensional Yang-Mills and symmetric product orbifolds
๐ London
Shota Komatsu
(CERN)
Abstract:
We propose a (bosonic) worldsheet description of two-dimensional Yang-Mills. We also argue that similar worldsheet actions provide candidate duals to the symmetric product orbifolds for arbitrary seed CFTs.
We propose a (bosonic) worldsheet description of two-dimensional Yang-Mills. We also argue that similar worldsheet actions provide candidate duals to the symmetric product orbifolds for arbitrary seed CFTs.
Posted by: QMW
Wed
5 Apr 2023
TBA
๐ London
Alexander Zhiboedov
(CERN)
Mon
3 Apr 2023
Cosmological solutions to the semiclassical Einstein equation with Minkowski-like vacua
๐ London
Nicolai Rothe
(TU Berlin)
Abstract:
We will discuss some newly found solutions to the full massless semiclassical Einstein equation (SCE) in a cosmological setting (with รโบ=0). After a short introduction to the relevant notions we present the SCE in a particular shape which allows for the construction of certain vacuum states. These states may be viewed as the least possible generalization of the Minkowski vacuum to general (cosmological) space-times. In this setting, solving the SCE breaks down into solving a certain ODE which can be approached numerically and, at least generically, we obtain solutions that well fit physical expectations. Moreover, these solutions indicate dark energy as a quantum effect back-reacting on cosmological metrics and, since in our model m=รโบ=0, this may not be traced back to the usual, obvious dark-energy/cosmological constant effect of a quantum field. Also we will shortly discuss some more physical problems that can be solved by our model.
We will discuss some newly found solutions to the full massless semiclassical Einstein equation (SCE) in a cosmological setting (with รโบ=0). After a short introduction to the relevant notions we present the SCE in a particular shape which allows for the construction of certain vacuum states. These states may be viewed as the least possible generalization of the Minkowski vacuum to general (cosmological) space-times. In this setting, solving the SCE breaks down into solving a certain ODE which can be approached numerically and, at least generically, we obtain solutions that well fit physical expectations. Moreover, these solutions indicate dark energy as a quantum effect back-reacting on cosmological metrics and, since in our model m=รโบ=0, this may not be traced back to the usual, obvious dark-energy/cosmological constant effect of a quantum field. Also we will shortly discuss some more physical problems that can be solved by our model.
Posted by: andrea
March 2023
Thu
30 Mar 2023
A CFT perspective on AdS amplitudes
๐ London
Agnese Bissi
(ICTP)
Abstract:
In this talk I will discuss how to compute amplitudes on AdS, using the analytic conformal bootstrap and the AdS/CFT correspondence. I will also discuss how to include higher trace operators in a simplified setup.
In this talk I will discuss how to compute amplitudes on AdS, using the analytic conformal bootstrap and the AdS/CFT correspondence. I will also discuss how to include higher trace operators in a simplified setup.
Posted by: QMW
Wed
29 Mar 2023
AdS Virasoro-Shapiro from dispersive sum rules and single valued multiple zeta values
๐ London
Joao Silva
(University of Oxford)
Abstract:
We study the four point correlator of the stress-energy tensor in N=4 SYM at leading order in inverse powers of the central charge. This corresponds to the Anti-deSitter version of the Virasoro-Shapiro amplitude. At large t'Hooft coupling lambda, we use dispersive sum rules to relate the Wilson coefficients in a 1/lambda expansion to the OPE data of heavy string operators. Assuming that the Wilson coefficients are in the ring of single valued multiple zeta values (as is expected for closed string amplitudes), we solve the dispersion relations to get the first 1/R^2 correction to the flat space amplitude.
We study the four point correlator of the stress-energy tensor in N=4 SYM at leading order in inverse powers of the central charge. This corresponds to the Anti-deSitter version of the Virasoro-Shapiro amplitude. At large t'Hooft coupling lambda, we use dispersive sum rules to relate the Wilson coefficients in a 1/lambda expansion to the OPE data of heavy string operators. Assuming that the Wilson coefficients are in the ring of single valued multiple zeta values (as is expected for closed string amplitudes), we solve the dispersion relations to get the first 1/R^2 correction to the flat space amplitude.
Posted by: andrea
Wed
29 Mar 2023
Large N factorization and holography
Alberto Zaffaroni
(University of Milano-Bicocca)
Abstract:
There has been some recent progress in understanding the microscopic derivation of the entropy of supersymmetric AdS black holes using holography and a localisation computation in the dual quantum field theory. In this talk, after a general discussion of the overall picture, I discuss the large N factorization properties of supersymmetric partition functions for CFT with a holographic dual in various dimensions. I show how this factorization is related to a universal gluing formula for the entropy functionals of known AdS black holes in terms of elementary objects called gravitational blocks.
There has been some recent progress in understanding the microscopic derivation of the entropy of supersymmetric AdS black holes using holography and a localisation computation in the dual quantum field theory. In this talk, after a general discussion of the overall picture, I discuss the large N factorization properties of supersymmetric partition functions for CFT with a holographic dual in various dimensions. I show how this factorization is related to a universal gluing formula for the entropy functionals of known AdS black holes in terms of elementary objects called gravitational blocks.
Posted by: IC2
Tue
28 Mar 2023
Decoupling limits in Renormalizable Quantum Gravity
Luca Buoninfante
(Nordita)
Abstract:
A natural way to extend Einstein's General Relativity in the high-energy regime is to introduce higher-order curvature terms in the gravitational Lagrangian. Indeed, by working in the framework of perturbative QFT one can show that quadratic-curvature gravity in four dimensions is strictly renormalizable. The quadratic-curvature terms are multiplied by dimensionless parameters that are related to the masses of the additional gravitational degrees of freedom and to the interaction couplings. In this talk, after having motivated Renormalizable Quantum Gravity, we will study the limits in which those dimensionless parameters tend to zero or to infinity, and show that different types of decoupling can occur. In particular, it will be shown that the presence of a non-zero cosmological constant affects the decoupling in a non-trivial way in the limit where the coefficient of the Weyl-squared term tends to infinity. We will discuss possible physical implications of this mathematical analysis for the high-energy behavior of the spin-2 massive ghost and for the classical limit of the theory. Several concepts that have been developed in the context of massive gravity will naturally emerge in this talk, sometimes with different relevance.
A natural way to extend Einstein's General Relativity in the high-energy regime is to introduce higher-order curvature terms in the gravitational Lagrangian. Indeed, by working in the framework of perturbative QFT one can show that quadratic-curvature gravity in four dimensions is strictly renormalizable. The quadratic-curvature terms are multiplied by dimensionless parameters that are related to the masses of the additional gravitational degrees of freedom and to the interaction couplings. In this talk, after having motivated Renormalizable Quantum Gravity, we will study the limits in which those dimensionless parameters tend to zero or to infinity, and show that different types of decoupling can occur. In particular, it will be shown that the presence of a non-zero cosmological constant affects the decoupling in a non-trivial way in the limit where the coefficient of the Weyl-squared term tends to infinity. We will discuss possible physical implications of this mathematical analysis for the high-energy behavior of the spin-2 massive ghost and for the classical limit of the theory. Several concepts that have been developed in the context of massive gravity will naturally emerge in this talk, sometimes with different relevance.
Posted by: IC
Mon
27 Mar 2023
LonTI: Geometry and fluxes
Daniel Waldram
(Imperial College)
Abstract:
Special geometries, such as Calabi-Yau manifolds, play a central role in multiple areas of string theory, as well as gravitational theories more generally. The goal of these lectures is to introduce some of the formalism and tools useful for characterising such geometries, pitched at the level of a starting PhD student. We will start with purely geometrical backgrounds using the general notions of a G-structure and special holonomy and then will go on to describe backgrounds that also have non-trivial fluxes. We will be guided by applications to string phenomenology and the AdS/cft correspondence.
Special geometries, such as Calabi-Yau manifolds, play a central role in multiple areas of string theory, as well as gravitational theories more generally. The goal of these lectures is to introduce some of the formalism and tools useful for characterising such geometries, pitched at the level of a starting PhD student. We will start with purely geometrical backgrounds using the general notions of a G-structure and special holonomy and then will go on to describe backgrounds that also have non-trivial fluxes. We will be guided by applications to string phenomenology and the AdS/cft correspondence.
Posted by: lonti
Thu
23 Mar 2023
Kaluza-Klein Spectrometry for String Theory Compactifications
Emanuel Malek
(Humboldt University of Berlin)
Abstract:
I will present a powerful new method that for the first time allows us to compute the Kaluza-Klein spectrum of a large class of string theory compactifications, including those arising in maximal gauged supergravities and beyond. This includes geometries with little to no remaining (super-)symmetries, completely inaccessible by previous methods. I will show how these insights can be used to holographically compute the anomalous dimensions of protected and unprotected operators in strongly-coupled CFTs, as well as to study global properties of their conformal manifolds. I will also show how the method can be used to determine the perturbative stability of non-supersymmetric AdS vacua. We will see the importance of higher Kaluza-Klein modes to the physics of string compactifications, e.g. in realising the compactness of moduli spaces, restoring supersymmetry that is lost in a consistent truncation, and in destabilising vacua that appear to stable in lower-dimensional supergravities.
I will present a powerful new method that for the first time allows us to compute the Kaluza-Klein spectrum of a large class of string theory compactifications, including those arising in maximal gauged supergravities and beyond. This includes geometries with little to no remaining (super-)symmetries, completely inaccessible by previous methods. I will show how these insights can be used to holographically compute the anomalous dimensions of protected and unprotected operators in strongly-coupled CFTs, as well as to study global properties of their conformal manifolds. I will also show how the method can be used to determine the perturbative stability of non-supersymmetric AdS vacua. We will see the importance of higher Kaluza-Klein modes to the physics of string compactifications, e.g. in realising the compactness of moduli spaces, restoring supersymmetry that is lost in a consistent truncation, and in destabilising vacua that appear to stable in lower-dimensional supergravities.
Posted by: IC2
Thu
23 Mar 2023
Log-CFTs, Skyrmions, and Quivers from 3d N=2 theories
๐ London
Sergei Gukov
(DIAS)
Abstract:
In this talk we will explore a class of 3d N=2 theories labeled by graphs and related to quivers in an unusual way. Unlike quiver gauge theories –- a class of Lagrangian field theories widely used in modern QFT –- theories that we consider are non-Lagrangian, in a sense that they can be defined as IR fixed points of gauge fields coupled to non-linear matter as in the Skyrme models of nuclei. Just like the physics of the Skyrme model is intimately tied to symmetries of QCD, generalized symmetries play an important role in these 3d N=2 theories. The connection to quivers, on the other hand, arises in a way that is not standard in modern particle physics, but is standard in the study of logarithmic CFTs and motivic DT invariants.
Download Mathematica demonstration here: theory.caltech.edu/~gukov/Plumbed.nb
3d Modularity software: https://github.com/d-passaro/pySeifert
In this talk we will explore a class of 3d N=2 theories labeled by graphs and related to quivers in an unusual way. Unlike quiver gauge theories –- a class of Lagrangian field theories widely used in modern QFT –- theories that we consider are non-Lagrangian, in a sense that they can be defined as IR fixed points of gauge fields coupled to non-linear matter as in the Skyrme models of nuclei. Just like the physics of the Skyrme model is intimately tied to symmetries of QCD, generalized symmetries play an important role in these 3d N=2 theories. The connection to quivers, on the other hand, arises in a way that is not standard in modern particle physics, but is standard in the study of logarithmic CFTs and motivic DT invariants.
Download Mathematica demonstration here: theory.caltech.edu/~gukov/Plumbed.nb
3d Modularity software: https://github.com/d-passaro/pySeifert
Posted by: QMW
Wed
22 Mar 2023
On anomalies and gauging of U(1) non-invertible symmetries in 4d QED
๐ London
Avner Karasik
(Cambridge University)
Abstract:
Abstract: I will present a way to promote the anomalous axial U(1) in 4d QED to an exact symmetry, with the price of losing its invertibility. I will then discuss some applications of this non-invertible U(1) symmetry. In particular, I will show how to couple this non-invertible symmetry to a gauge field. By taking this gauge field to be dynamical, we get a new type of gauge theory with unconventional interactions and constraints. By taking this gauge field to be background, we can study 't-Hooft anomalies of the non-invertible symmetry.
Abstract: I will present a way to promote the anomalous axial U(1) in 4d QED to an exact symmetry, with the price of losing its invertibility. I will then discuss some applications of this non-invertible U(1) symmetry. In particular, I will show how to couple this non-invertible symmetry to a gauge field. By taking this gauge field to be dynamical, we get a new type of gauge theory with unconventional interactions and constraints. By taking this gauge field to be background, we can study 't-Hooft anomalies of the non-invertible symmetry.
Posted by: QMW
Mon
20 Mar 2023
LonTI: Geometry and fluxes
Daniel Waldram
(Imperial College)
Abstract:
รขโฌลSpecialรขโฌย geometries, such as Calabi-Yau manifolds, play a central role in multiple areas of string theory, as well as gravitational theories more generally. The goal of these lectures is to introduce some of the formalism and tools useful for characterising such geometries, pitched at the level of a starting PhD student. We will start with purely geometrical backgrounds using the general notions of a G-structure and special holonomy and then will go on to describe backgrounds that also have non-trivial fluxes. We will be guided by applications to string phenomenology and the AdS/cft correspondence.
รขโฌลSpecialรขโฌย geometries, such as Calabi-Yau manifolds, play a central role in multiple areas of string theory, as well as gravitational theories more generally. The goal of these lectures is to introduce some of the formalism and tools useful for characterising such geometries, pitched at the level of a starting PhD student. We will start with purely geometrical backgrounds using the general notions of a G-structure and special holonomy and then will go on to describe backgrounds that also have non-trivial fluxes. We will be guided by applications to string phenomenology and the AdS/cft correspondence.
Posted by: CityU2
Mon
20 Mar 2023
Computing anomalous dimensions of strongly-coupled CFTs from supergravity
๐ London
Emanuel Malek
(Humboldt)
Abstract:
I will present a powerful new method that for the first time allows us to compute the Kaluza-Klein spectrum of a large class of string theory compactifications, including those arising in maximal gauged supergravities and beyond. This includes geometries with little to no remaining (super-)symmetries, completely inaccessible by previous methods. I will show how these insights can be used to holographically compute the anomalous dimensions of protected and unprotected operators in strongly-coupled CFTs, as well as to study global properties of their conformal manifolds. I will also show how the method can be used to determine the perturbative stability of non-supersymmetric AdS vacua. We will see the importance of higher Kaluza-Klein modes to the physics of string compactifications, e.g. in realising the compactness of moduli spaces, restoring supersymmetry that is lost in a consistent truncation, and in destabilising non-supersymmetric vacua that appear to stable in lower-dimensional supergravities.
I will present a powerful new method that for the first time allows us to compute the Kaluza-Klein spectrum of a large class of string theory compactifications, including those arising in maximal gauged supergravities and beyond. This includes geometries with little to no remaining (super-)symmetries, completely inaccessible by previous methods. I will show how these insights can be used to holographically compute the anomalous dimensions of protected and unprotected operators in strongly-coupled CFTs, as well as to study global properties of their conformal manifolds. I will also show how the method can be used to determine the perturbative stability of non-supersymmetric AdS vacua. We will see the importance of higher Kaluza-Klein modes to the physics of string compactifications, e.g. in realising the compactness of moduli spaces, restoring supersymmetry that is lost in a consistent truncation, and in destabilising non-supersymmetric vacua that appear to stable in lower-dimensional supergravities.
Posted by: andrea
Thu
16 Mar 2023
Classification of Superconformal field theories in four dimensions
๐ London
Mario Martone
(KCL)
Abstract:
In this talk I will give you an update of the status of the classification
of superconformal field theories in four dimensions. After reviewing the basic
properties which make the classification of theories with both supersymmetry
and conformal invariance possible, I will describe in detail the framework which
allows for a bottom up analysis and summarise the latest results in rank-2.
In this talk I will give you an update of the status of the classification
of superconformal field theories in four dimensions. After reviewing the basic
properties which make the classification of theories with both supersymmetry
and conformal invariance possible, I will describe in detail the framework which
allows for a bottom up analysis and summarise the latest results in rank-2.
Posted by: QMW
Tue
14 Mar 2023
Non-perturbative strings, asymptotic safety, and the swampland
Alessia Platania
(Perimeter Institute for Theoretical Physics)
Abstract:
Quantum gravity is undoubtfully one of the most important missing pieces in the understanding of the mathematical structure of our universe.
The impossibility of consistently quantizing gravity via perturbative quantum field theory has led to a plethora of different proposals, from asymptotically safe gravity to non-local gravity, loop quantum gravity, and string theory. Different approaches face different problems and have succeeded in different areas. Yet, on the conceptual side, it is not obvious that all these frameworks are inequivalent or unrelated: some theories may be low-energy approximations of others, or could even provide different mathematical descriptions of the same physics. On the technical side, the knowledge gained in an approach could be useful to investigate certain aspects of others.
In this spirit, I will review progress in connecting and contrasting two theories: asymptotically safe gravity and string theory. Specifically, I will discuss how to test asymptotic safety using stringy swampland constraints, and how techniques developed in the context of asymptotically safe gravity can be exploited to compute cosmological higher-derivative corrections to all orders in string theory.
Quantum gravity is undoubtfully one of the most important missing pieces in the understanding of the mathematical structure of our universe.
The impossibility of consistently quantizing gravity via perturbative quantum field theory has led to a plethora of different proposals, from asymptotically safe gravity to non-local gravity, loop quantum gravity, and string theory. Different approaches face different problems and have succeeded in different areas. Yet, on the conceptual side, it is not obvious that all these frameworks are inequivalent or unrelated: some theories may be low-energy approximations of others, or could even provide different mathematical descriptions of the same physics. On the technical side, the knowledge gained in an approach could be useful to investigate certain aspects of others.
In this spirit, I will review progress in connecting and contrasting two theories: asymptotically safe gravity and string theory. Specifically, I will discuss how to test asymptotic safety using stringy swampland constraints, and how techniques developed in the context of asymptotically safe gravity can be exploited to compute cosmological higher-derivative corrections to all orders in string theory.
Posted by: IC
Mon
13 Mar 2023
LonTI: Geometry and fluxes
Daniel Waldram
(Imperial College)
Abstract:
Special geometries, such as Calabi-Yau manifolds, play a central role in multiple areas of string theory, as well as gravitational theories more generally. The goal of these lectures is to introduce some of the formalism and tools useful for characterising such geometries, pitched at the level of a starting PhD student. We will start with purely geometrical backgrounds using the general notions of a G-structure and special holonomy and then will go on to describe backgrounds that also have non-trivial fluxes. We will be guided by applications to string phenomenology and the AdS/cft correspondence.
Special geometries, such as Calabi-Yau manifolds, play a central role in multiple areas of string theory, as well as gravitational theories more generally. The goal of these lectures is to introduce some of the formalism and tools useful for characterising such geometries, pitched at the level of a starting PhD student. We will start with purely geometrical backgrounds using the general notions of a G-structure and special holonomy and then will go on to describe backgrounds that also have non-trivial fluxes. We will be guided by applications to string phenomenology and the AdS/cft correspondence.
Posted by: CityU2
Mon
13 Mar 2023
LonTI Special Event. Tesco: From pen and paper to machine learning
Sebastian Lautz
(Tesco)
Abstract:
In this talk, I will outline how I went from solving Killing spinor equations with pen and paper to a career in coding-intensive Data Science. I'll talk about my experience of working as a Data Scientist for Tesco and how leaving academia didn't mean the end of doing research for me.
Bio: Sebastian completed his PhD in Theoretical Physics at King's in 2019. He then transitioned from the less big data-driven classification of SUGRA backgrounds to a career in computationally heavy machine learning. Since 2020, he's been working as a (by now) Senior Data Scientist at Tesco where he mainly works within the Price Optimisation space and looks after collaborations with academia.
In this talk, I will outline how I went from solving Killing spinor equations with pen and paper to a career in coding-intensive Data Science. I'll talk about my experience of working as a Data Scientist for Tesco and how leaving academia didn't mean the end of doing research for me.
Bio: Sebastian completed his PhD in Theoretical Physics at King's in 2019. He then transitioned from the less big data-driven classification of SUGRA backgrounds to a career in computationally heavy machine learning. Since 2020, he's been working as a (by now) Senior Data Scientist at Tesco where he mainly works within the Price Optimisation space and looks after collaborations with academia.
Posted by: CityU2
Mon
13 Mar 2023
Reconstructing Gauge Group from OPE Coefficients
๐ London
Rajath Radhakrishnan
(ICTP Trieste)
Abstract:
The structure of the gauge group constrains the properties of operators in a G-gauge theory. In this talk, I will consider the reverse direction and ask what properties of a (finite) gauge group can be reconstructed from the operators. I will first consider OPE/fusion rules of Wilson lines and explain various properties of the gauge group that can be reconstructed from it. Then I will introduce certain surface operators which exist in any G-gauge theory. I will describe the fusion rules of these surface operators and show that, in general, there are properties of the gauge group that can be deduced from the fusion rules of surface operators which cannot be obtained from the fusion rules of Wilson lines, and vice-versa.
The structure of the gauge group constrains the properties of operators in a G-gauge theory. In this talk, I will consider the reverse direction and ask what properties of a (finite) gauge group can be reconstructed from the operators. I will first consider OPE/fusion rules of Wilson lines and explain various properties of the gauge group that can be reconstructed from it. Then I will introduce certain surface operators which exist in any G-gauge theory. I will describe the fusion rules of these surface operators and show that, in general, there are properties of the gauge group that can be deduced from the fusion rules of surface operators which cannot be obtained from the fusion rules of Wilson lines, and vice-versa.
Posted by: QMW
Wed
8 Mar 2023
Symmetries of TTbar-deformed CFTs and their holographic avatars
๐ London
Monica Guica
(IPhT, Saclay)
Abstract:
I will discuss the classical and quantum symmetries of TTbar-deformed CFTs and their manifestations in holography. These symmetries are infinite in number and, in a certain basis, organise into a Virasoro x Virasoro algebra with the same central charge as that of the undeformed CFT. I will present a quantum, abstract proof of the existence of these symmetries and three different explicit classical perspectives: Hamiltonian, Lagrangian and holographic. I will then discuss the relationship between the single-trace TTbar deformation and the asymptotically linear dilaton background in string theory, and show that the asymptotic symmetries of this background take an identical form to those of TTbar-deformed CFTs, further strengthening this proposed connection.
I will discuss the classical and quantum symmetries of TTbar-deformed CFTs and their manifestations in holography. These symmetries are infinite in number and, in a certain basis, organise into a Virasoro x Virasoro algebra with the same central charge as that of the undeformed CFT. I will present a quantum, abstract proof of the existence of these symmetries and three different explicit classical perspectives: Hamiltonian, Lagrangian and holographic. I will then discuss the relationship between the single-trace TTbar deformation and the asymptotically linear dilaton background in string theory, and show that the asymptotic symmetries of this background take an identical form to those of TTbar-deformed CFTs, further strengthening this proposed connection.
Posted by: oxford
Wed
8 Mar 2023
Towards Non-perturbative QFT in Infinite Volume: From Time Dependent Observables to Thermalization
๐ London
Emanuel Katz
(Boston)
Abstract:
I will describe progress in formulating and solving QFT non-perturbatively in the infinite volume limit using Hamiltonian Truncation. I will present new results for time-dependent observables in a certain class of both Lagrangian and non-Lagrangian theories in 1+1d. I will also present our study of chaos and thermalization for a scalar theory, where we test the Eigenstate Thermalization Hypothesis (ETH). While we do find results which are broadly consistent with ETH, at weak coupling we also find a set of รขโฌลscarรขโฌย states, which do not satisfy Random Matrix Statistics, and which can be distinguished from the rest of the thermal states by the expectation value of local operators.
I will describe progress in formulating and solving QFT non-perturbatively in the infinite volume limit using Hamiltonian Truncation. I will present new results for time-dependent observables in a certain class of both Lagrangian and non-Lagrangian theories in 1+1d. I will also present our study of chaos and thermalization for a scalar theory, where we test the Eigenstate Thermalization Hypothesis (ETH). While we do find results which are broadly consistent with ETH, at weak coupling we also find a set of รขโฌลscarรขโฌย states, which do not satisfy Random Matrix Statistics, and which can be distinguished from the rest of the thermal states by the expectation value of local operators.
Posted by: oxford
Tue
7 Mar 2023
Quantum phenomena in the early Universe
Kimmo Kainulainen
(Helsinki Institute of Physics and University of Jyvaskyla)
Abstract:
Quantum coherence plays essential role in diverse phenomena of relevance in the early universe.
Examples include activation of sterile neutrinos, electroweak baryogenesis, resonant leptogenesis
and particle production in phase transitions and during the (p)reheating stage after inflation.
After a general introduction I will concentrate on the particle production problem. I will show
how one can derive coupled, renormalized and tractable quantum kinetic equations for the scalar
field 1- and 2-point functions starting from the CTP-formalism, working in the Hartree
approximation of the 2PI-action. I will then apply these equations to study particle production
and the back-reaction from the non-equilibrium modes on the dynamics of the one-point function.
We will see both spinodal and parametric resonances taking place and sometimes overlapping in a
novel way, and we follow the process of decoherence and thermalization. Overall, I argue that
advanced quantum transport equations are necessary for an accuarate description of many systems
of acute interest in cosmology.
Quantum coherence plays essential role in diverse phenomena of relevance in the early universe.
Examples include activation of sterile neutrinos, electroweak baryogenesis, resonant leptogenesis
and particle production in phase transitions and during the (p)reheating stage after inflation.
After a general introduction I will concentrate on the particle production problem. I will show
how one can derive coupled, renormalized and tractable quantum kinetic equations for the scalar
field 1- and 2-point functions starting from the CTP-formalism, working in the Hartree
approximation of the 2PI-action. I will then apply these equations to study particle production
and the back-reaction from the non-equilibrium modes on the dynamics of the one-point function.
We will see both spinodal and parametric resonances taking place and sometimes overlapping in a
novel way, and we follow the process of decoherence and thermalization. Overall, I argue that
advanced quantum transport equations are necessary for an accuarate description of many systems
of acute interest in cosmology.
Posted by: IC
Tue
7 Mar 2023
TBA
๐ London
Micha Berkooz
(Weizmann)
Thu
2 Mar 2023
Higher-dimensional origin of extended black hole thermodynamics
๐ London
Andrew Svesko
(University College London)
Abstract:
A key difference between black holes and ordinary thermal systems is the absence of a pressure-volume work term in the first law of black hole thermodynamics. It is possible to introduce such a work term for black holes in backgrounds with a cosmological constant by treating the cosmological constant as a pressure, offering a rich gravitational perspective on everyday phenomena. Missing, however, is justification for allowing variations of the cosmological constant. In this talk I will present a higher-dimensional origin of 'extended black hole thermodynamics' using holographic braneworlds. In this set-up, gravity is coupled to a lower-dimensional brane such that classical black holes in a bulk anti-de Sitter spacetime correspond to exact quantum corrected black holes localized on the brane, including all orders of semi-classical backreaction. Crucially, varying the tension of the brane leads to a dynamical cosmological constant on the brane, and, correspondingly, a variable pressure attributed to the brane black hole. In other words, standard thermodynamics of classical black holes induces extended thermodynamics of `quantum' black holes on a brane. As proof of concept, I will present the extended thermodynamics of the quantum BTZ black hole, also providing a microscopic interpretation using `double holographyรขโฌโข.
A key difference between black holes and ordinary thermal systems is the absence of a pressure-volume work term in the first law of black hole thermodynamics. It is possible to introduce such a work term for black holes in backgrounds with a cosmological constant by treating the cosmological constant as a pressure, offering a rich gravitational perspective on everyday phenomena. Missing, however, is justification for allowing variations of the cosmological constant. In this talk I will present a higher-dimensional origin of 'extended black hole thermodynamics' using holographic braneworlds. In this set-up, gravity is coupled to a lower-dimensional brane such that classical black holes in a bulk anti-de Sitter spacetime correspond to exact quantum corrected black holes localized on the brane, including all orders of semi-classical backreaction. Crucially, varying the tension of the brane leads to a dynamical cosmological constant on the brane, and, correspondingly, a variable pressure attributed to the brane black hole. In other words, standard thermodynamics of classical black holes induces extended thermodynamics of `quantum' black holes on a brane. As proof of concept, I will present the extended thermodynamics of the quantum BTZ black hole, also providing a microscopic interpretation using `double holographyรขโฌโข.
Posted by: QMW
Thu
2 Mar 2023
Carroll, Cotton and Ehlers
๐ London
Marios Petropoulos
(Ecole Polytechnique, CPHT)
Abstract:
Carroll geometries emerge as conformal boundaries of asymptotically flat spacetimes and have come to the forefront with the advent of flat holography. I will introduce these tools and show how they are used for unravelling the boundary manifestation of Ehlers' hidden Mรยถbius symmetry present in four-dimensional Ricci-flat spacetimes that enjoy a time-like isometry. This is achieved in a designated gauge, where the three-dimensional Carrollian nature of the null conformal boundary is manifest and covariantly implemented. The action of the Mรยถbius group is local on the space of Carrollian boundary data. Among these data, the Carrollian Cotton tensor plays a prominent role both in the Mรยถbius electric/magnetic duality and for the determination of charges.
Carroll geometries emerge as conformal boundaries of asymptotically flat spacetimes and have come to the forefront with the advent of flat holography. I will introduce these tools and show how they are used for unravelling the boundary manifestation of Ehlers' hidden Mรยถbius symmetry present in four-dimensional Ricci-flat spacetimes that enjoy a time-like isometry. This is achieved in a designated gauge, where the three-dimensional Carrollian nature of the null conformal boundary is manifest and covariantly implemented. The action of the Mรยถbius group is local on the space of Carrollian boundary data. Among these data, the Carrollian Cotton tensor plays a prominent role both in the Mรยถbius electric/magnetic duality and for the determination of charges.
Posted by: andrea
Wed
1 Mar 2023
Entropy functions for supersymmetric AdS Black Holes
๐ London
Jerome Gauntlett
(Imperial)
Abstract:
The talk summarises recent work that illuminates our understanding of
black hole entropy for supersymmetric black holes in Anti-de-Sitter space.
We consider supersymmetric \(AdS_3\times Y_7\) solutions of type IIB and
\(AdS_2\times Y_9\) solutions of \(D=11\) supergravity. These can arise as the
near horizon limit of black strings in \(AdS_5\) and and black holes in \(AdS_4\) spacetimes, respectively.
We explain how novel extremisation techniques enable one to compute physical observables
without explicitly solving Einstein equations. This allows one to identify infinite new classes of \(AdS_3\)/d=2 SCFT pairs, as well obtain a microstate counting interpretation for infinite classes of supersymmetric black holes in \(AdS_4\).
A sub-class of examples correspond to branes wrapping certain two-dimensional orbifolds known as spindles and this
has opened up a new direction in AdS/CFT with novel connections to accelerating black holes.
The talk summarises recent work that illuminates our understanding of
black hole entropy for supersymmetric black holes in Anti-de-Sitter space.
We consider supersymmetric \(AdS_3\times Y_7\) solutions of type IIB and
\(AdS_2\times Y_9\) solutions of \(D=11\) supergravity. These can arise as the
near horizon limit of black strings in \(AdS_5\) and and black holes in \(AdS_4\) spacetimes, respectively.
We explain how novel extremisation techniques enable one to compute physical observables
without explicitly solving Einstein equations. This allows one to identify infinite new classes of \(AdS_3\)/d=2 SCFT pairs, as well obtain a microstate counting interpretation for infinite classes of supersymmetric black holes in \(AdS_4\).
A sub-class of examples correspond to branes wrapping certain two-dimensional orbifolds known as spindles and this
has opened up a new direction in AdS/CFT with novel connections to accelerating black holes.
Posted by: andrea
February 2023
Fri
24 Feb 2023
Extended operators in 4d N=2 SCFTs and vertex algebras
๐ London
Matteo Lotito
(Seoul National U)
Abstract:
Local Schur operators in 4d N=2 SCFTs form a protected class of operators giving rise to a 2d vertex operator algebra.
Following the local operator picture, we introduce classes of conformal extended operators (lines, surfaces) and study these in twisted Schur cohomology.
We show how these operators support a more general algebraic structure compared to the local operators, giving rise to an extension of the vertex algebra known for local Schur operators.
Local Schur operators in 4d N=2 SCFTs form a protected class of operators giving rise to a 2d vertex operator algebra.
Following the local operator picture, we introduce classes of conformal extended operators (lines, surfaces) and study these in twisted Schur cohomology.
We show how these operators support a more general algebraic structure compared to the local operators, giving rise to an extension of the vertex algebra known for local Schur operators.
Posted by: andrea
Wed
22 Feb 2023
Extended operators in 4d N=2 SCFTs and vertex algebras
๐ London
Matteo Lotito
(SNU)
Abstract:
Local Schur operators in 4d N=2 SCFTs form a protected class of operators giving rise to a 2d vertex operator algebra. Following the local operator picture, we introduce classes of conformal extended operators (lines, surfaces) and study these in twisted Schur cohomology. We show how these operators support a vertex algebra structure, extending the VOA picture of local Schur operators.
Local Schur operators in 4d N=2 SCFTs form a protected class of operators giving rise to a 2d vertex operator algebra. Following the local operator picture, we introduce classes of conformal extended operators (lines, surfaces) and study these in twisted Schur cohomology. We show how these operators support a vertex algebra structure, extending the VOA picture of local Schur operators.
Posted by: QMW
Wed
22 Feb 2023
Keeping matter in the loop in de Sitter quantum gravity
๐ London
Jackson Fliss
(University of Cambridge)
Abstract:
Chern-Simons (CS) theory provides an attractive framework for quantizing 3d gravity, at least around a fixed saddle-point. But how do we describe matter in CS gravity while retaining its useful features? In this talk I will focus on the CS description of Euclidean de Sitter space about its three-sphere saddle. I will introduce a "Wilson spool," which can be interpreted as a collection of Wilson loops winding arbitrarily many times around the three-sphere and which provides an effective description of massive one-loop determinants. Constructing and subsequently evaluating the spool will require us to revisit starting assumptions about unitarity of the representations appearing in the Wilson loops as well as the library of "exact methods" available to CS theories on the three-sphere. The result will be an object that reduces to the scalar one-loop determinant on the three-sphere in the limit that Newton's constant vanishes yet can be evaluated at in any order in G_N perturbation theory. Time remaining, I will either discuss potential further applications of the Wilson spool (either to spinning fields or to contexts outside of de Sitter) or (unresolved) implications of CS gravity for the dS/CFT dictionary.
Chern-Simons (CS) theory provides an attractive framework for quantizing 3d gravity, at least around a fixed saddle-point. But how do we describe matter in CS gravity while retaining its useful features? In this talk I will focus on the CS description of Euclidean de Sitter space about its three-sphere saddle. I will introduce a "Wilson spool," which can be interpreted as a collection of Wilson loops winding arbitrarily many times around the three-sphere and which provides an effective description of massive one-loop determinants. Constructing and subsequently evaluating the spool will require us to revisit starting assumptions about unitarity of the representations appearing in the Wilson loops as well as the library of "exact methods" available to CS theories on the three-sphere. The result will be an object that reduces to the scalar one-loop determinant on the three-sphere in the limit that Newton's constant vanishes yet can be evaluated at in any order in G_N perturbation theory. Time remaining, I will either discuss potential further applications of the Wilson spool (either to spinning fields or to contexts outside of de Sitter) or (unresolved) implications of CS gravity for the dS/CFT dictionary.
Posted by: andrea
Mon
20 Feb 2023
LonTI: Introduction to CFT and Conformal Bootstrap
Andreas Stergiou
(King's College)
Abstract:
These lectures aim to provide a self-contained introduction to the modern conformal bootstrap method. The study of conformal field theory (CFT) will first be motivated and the รขโฌลoldรขโฌย way of studying CFTs as endpoints of RG flows will be explained. The set of ideas necessary to understand the conformal bootstrap method will then be introduced, and both analytic and numerical implementations of the conformal bootstrap method will be discussed.
These lectures aim to provide a self-contained introduction to the modern conformal bootstrap method. The study of conformal field theory (CFT) will first be motivated and the รขโฌลoldรขโฌย way of studying CFTs as endpoints of RG flows will be explained. The set of ideas necessary to understand the conformal bootstrap method will then be introduced, and both analytic and numerical implementations of the conformal bootstrap method will be discussed.
Posted by: CityU2
Mon
20 Feb 2023
Locality of higher-spin gravity in de Sitter vs. Anti-de Sitter space
๐ London
Yasha Neiman
(OIST)
Abstract:
Higher-spin gravity is a curious beast of mathematical physics: a cousin of supergravity and string theory that seems comfortable with 4 spacetime dimensions and positive cosmological constant.
On the other hand, general arguments show that this theory must be pathologically non-local at quartic order. In this talk, I claim that the non-locality arguments rely on Lorentzian boundary signature. For Euclidean boundary, explicit calculation shows that the feared non-locality is absent. This implies that the theory is healthy in de Sitter space, but not in (Lorentzian) AdS. The surprising possibility of such signature-dependent locality has long been implicit in the CFT/holography literature. Higher-spin gravity provides the first explicit example.
Higher-spin gravity is a curious beast of mathematical physics: a cousin of supergravity and string theory that seems comfortable with 4 spacetime dimensions and positive cosmological constant.
On the other hand, general arguments show that this theory must be pathologically non-local at quartic order. In this talk, I claim that the non-locality arguments rely on Lorentzian boundary signature. For Euclidean boundary, explicit calculation shows that the feared non-locality is absent. This implies that the theory is healthy in de Sitter space, but not in (Lorentzian) AdS. The surprising possibility of such signature-dependent locality has long been implicit in the CFT/holography literature. Higher-spin gravity provides the first explicit example.
Posted by: andrea
Wed
15 Feb 2023
Tilting Space of Boundary Conformal Field Theories
๐ London
Vladimir Schaub
(KCL)
Abstract:
I will explain how, in boundary conformal field theories, global symmetries broken by boundary conditions generate a homogeneous conformal manifold. These manifolds are cosets, and I will give fully two worked out examples in the case of free fields of spin zero and one-half. These results give simple illustrations of the salient features of conformal manifolds, which I will review, while generalising to interacting setups.
I will explain how, in boundary conformal field theories, global symmetries broken by boundary conditions generate a homogeneous conformal manifold. These manifolds are cosets, and I will give fully two worked out examples in the case of free fields of spin zero and one-half. These results give simple illustrations of the salient features of conformal manifolds, which I will review, while generalising to interacting setups.
Posted by: QMW
Mon
13 Feb 2023
LonTI: Introduction to CFT and Conformal Bootstrap
Andreas Stergiou
(King's College)
Abstract:
These lectures aim to provide a self-contained introduction to the modern conformal bootstrap method. The study of conformal field theory (CFT) will first be motivated and the รขโฌลoldรขโฌย way of studying CFTs as endpoints of RG flows will be explained. The set of ideas necessary to understand the conformal bootstrap method will then be introduced, and both analytic and numerical implementations of the conformal bootstrap method will be discussed.
These lectures aim to provide a self-contained introduction to the modern conformal bootstrap method. The study of conformal field theory (CFT) will first be motivated and the รขโฌลoldรขโฌย way of studying CFTs as endpoints of RG flows will be explained. The set of ideas necessary to understand the conformal bootstrap method will then be introduced, and both analytic and numerical implementations of the conformal bootstrap method will be discussed.
Posted by: CityU2
Mon
13 Feb 2023
Dissipation of oscillating homogeneous scalar condensates - unusual day and time
Wenyuan Ai
(Kings College London)
Abstract:
Scalar condensates are very common objects in cosmology. For example, the inflaton field can be viewed as a scalar condensate before it completely dissipates into ordinary particles during reheating. Axion condensates may have been formed through the vacuum-misalignment mechanism. In this talk, I will discuss the dissipation of oscillating homogeneous scalar backgrounds in flat spacetime and an expanding universe using nonequilibrium quantum field theory. The latter naturally captures the thermal effects and backreaction effects. For quasi-harmonic oscillations, we adopt the multi-scale analysis to obtain analytical approximate expressions for the self-consistent evolution of the scalar condensates in terms of the retarded self-energy and retarded proper four-vertex function, whose imaginary parts characterize different condensate decay channels. At finite temperatures, there are many new condensate decay channels that would be absent at zero temperature. These new channels could play an important role in ensuring a complete dissipation in an expanding universe.
The talk is based on the following two papers: JHEP 11 (2021) 160 [arXiv:2108.00254 [hep-ph]]; JHEP 11 (2022) 075 [arXiv:2202.08218 [hep-ph]]
Scalar condensates are very common objects in cosmology. For example, the inflaton field can be viewed as a scalar condensate before it completely dissipates into ordinary particles during reheating. Axion condensates may have been formed through the vacuum-misalignment mechanism. In this talk, I will discuss the dissipation of oscillating homogeneous scalar backgrounds in flat spacetime and an expanding universe using nonequilibrium quantum field theory. The latter naturally captures the thermal effects and backreaction effects. For quasi-harmonic oscillations, we adopt the multi-scale analysis to obtain analytical approximate expressions for the self-consistent evolution of the scalar condensates in terms of the retarded self-energy and retarded proper four-vertex function, whose imaginary parts characterize different condensate decay channels. At finite temperatures, there are many new condensate decay channels that would be absent at zero temperature. These new channels could play an important role in ensuring a complete dissipation in an expanding universe.
The talk is based on the following two papers: JHEP 11 (2021) 160 [arXiv:2108.00254 [hep-ph]]; JHEP 11 (2022) 075 [arXiv:2202.08218 [hep-ph]]
Posted by: IC
Thu
9 Feb 2023
The Geometry behind Scattering Amplitudes
๐ London
Livia Ferro
(University of Hertfordshire)
Abstract:
In recent years it has become clear that particular geometric structures, called positive geometries, underlie various observables in quantum field theories. In this talk I will review this connection for scattering amplitudes. After a broad review of the main ingredients involved, I will focus on maximally supersymmetric Yang-Mills theory and discuss a positive geometry encoding scattering processes in this theory – the momentum amplituhedron. In particular, I will show how such geometry encodes the properties of amplitudes. Finally, I will discuss some of the questions which remain open in this framework.
In recent years it has become clear that particular geometric structures, called positive geometries, underlie various observables in quantum field theories. In this talk I will review this connection for scattering amplitudes. After a broad review of the main ingredients involved, I will focus on maximally supersymmetric Yang-Mills theory and discuss a positive geometry encoding scattering processes in this theory – the momentum amplituhedron. In particular, I will show how such geometry encodes the properties of amplitudes. Finally, I will discuss some of the questions which remain open in this framework.
Posted by: QMW
Wed
8 Feb 2023
Thermalization and Chaos in 1+1d QFTs
๐ London
Luca Delacretaz
(University of Chicago)
Abstract:
Nonintegrable QFTs are expected to thermalize and exhibit emergence of hydrodynamics and chaos. In weakly coupled QFTs, kinetic theory captures local thermalization; such a versatile tool is absent away from the perturbative regime. I will present analytical and numerical results using nonperturbative methods to study thermalization at strong coupling. I will show how requiring causality in the thermal state leads to strong analytic constraints on the thermodynamics and out-of-equilibrium properties of any relativistic 1+1d QFT. I will then discuss Lightcone Conformal Truncation (LCT) as a powerful numerical tool to study thermalization of QFTs. Applied to \phi^4 theory in 1+1d, LCT reveals eigenstate thermalization and onset of random matrix universality at any nonzero coupling. Finally, I will discuss prospects for observing the emergence of hydrodynamics in QFTs using Hamiltonian truncation. (Based on: https://arxiv.org/abs/2207.11261 and https://arxiv.org/abs/2105.02229).
Nonintegrable QFTs are expected to thermalize and exhibit emergence of hydrodynamics and chaos. In weakly coupled QFTs, kinetic theory captures local thermalization; such a versatile tool is absent away from the perturbative regime. I will present analytical and numerical results using nonperturbative methods to study thermalization at strong coupling. I will show how requiring causality in the thermal state leads to strong analytic constraints on the thermodynamics and out-of-equilibrium properties of any relativistic 1+1d QFT. I will then discuss Lightcone Conformal Truncation (LCT) as a powerful numerical tool to study thermalization of QFTs. Applied to \phi^4 theory in 1+1d, LCT reveals eigenstate thermalization and onset of random matrix universality at any nonzero coupling. Finally, I will discuss prospects for observing the emergence of hydrodynamics in QFTs using Hamiltonian truncation. (Based on: https://arxiv.org/abs/2207.11261 and https://arxiv.org/abs/2105.02229).
Posted by: andrea
Tue
7 Feb 2023
Causal Set Quantum Gravity and the Hard Problem of Consciousness
Fay Dowker
(Imperial College London)
Abstract:
In this talk I will develop Rafael D. Sorkinรขโฌโขs heuristic that a partially ordered process of the birth of spacetime atoms in causal set quantum gravity can provide an objective physical correlate of our perception of time passing. I will argue that one cannot have an external, fully objective picture of the birth process because the order in which the spacetime atoms are born is a partial order. I propose that live experience in causal set theory is an internal รขโฌลviewรขโฌย of the objective birth process in which events that are neural correlates of consciousness occur. In causal set theory, what รขโฌลbreathes fireรขโฌย into a neural correlate of consciousness is that which breathes fire into the whole universe: the unceasing, partially ordered process of the birth of spacetime atoms.
In this talk I will develop Rafael D. Sorkinรขโฌโขs heuristic that a partially ordered process of the birth of spacetime atoms in causal set quantum gravity can provide an objective physical correlate of our perception of time passing. I will argue that one cannot have an external, fully objective picture of the birth process because the order in which the spacetime atoms are born is a partial order. I propose that live experience in causal set theory is an internal รขโฌลviewรขโฌย of the objective birth process in which events that are neural correlates of consciousness occur. In causal set theory, what รขโฌลbreathes fireรขโฌย into a neural correlate of consciousness is that which breathes fire into the whole universe: the unceasing, partially ordered process of the birth of spacetime atoms.
Posted by: IC
Mon
6 Feb 2023
LonTI: Introduction to CFT and Conformal Bootstrap
Andreas Stergiou
(King's College)
Abstract:
These lectures aim to provide a self-contained introduction to the modern conformal bootstrap method. The study of conformal field theory (CFT) will first be motivated and the รขโฌลoldรขโฌย way of studying CFTs as endpoints of RG flows will be explained. The set of ideas necessary to understand the conformal bootstrap method will then be introduced, and both analytic and numerical implementations of the conformal bootstrap method will be discussed.
These lectures aim to provide a self-contained introduction to the modern conformal bootstrap method. The study of conformal field theory (CFT) will first be motivated and the รขโฌลoldรขโฌย way of studying CFTs as endpoints of RG flows will be explained. The set of ideas necessary to understand the conformal bootstrap method will then be introduced, and both analytic and numerical implementations of the conformal bootstrap method will be discussed.
Posted by: CityU2
Mon
6 Feb 2023
Dynamical consequences of 1-form and 2-group symmetries in Argyres-Douglas theories
๐ London
Alessandro Mininno
(Hamburg)
Abstract:
In this talk, I will discuss the dynamical consequences of having 1-form and 2-group symmetries in Argyres-Douglas (AD) theories, particularly focusing on D_p(G) theories.
I will first review how to construct (G,G') and D_p(G) theories from geometric engineering. Then, I will briefly review how 1-form symmetries are found in these AD theories, focusing on their dynamical consequences in the study of the Higgs branch for such theories. Analogously, I will show how certain D_p(G) theories enjoy a 2-group structure due to a non-trivial extension between a discrete 1-form symmetry and a continuous 0-form symmetry, emphasizing the dynamical consequences that a 2-group structure entails, and the family of AD theories that have it.
If time permits it, I will show that it is possible to obtain an infinite family of AD theories starting from an arbitrary D_p(G) theory, where the theories in the same family share some properties. We called this "bootstrapping" of D_p(G) theories. The bootstrapping is also visible at the level of the 3d mirror theories of the D_p(G).
My results are based mainly on arXiv:2203.16550 [hep-th] and arXiv:2208.11130 [hep-th].
In this talk, I will discuss the dynamical consequences of having 1-form and 2-group symmetries in Argyres-Douglas (AD) theories, particularly focusing on D_p(G) theories.
I will first review how to construct (G,G') and D_p(G) theories from geometric engineering. Then, I will briefly review how 1-form symmetries are found in these AD theories, focusing on their dynamical consequences in the study of the Higgs branch for such theories. Analogously, I will show how certain D_p(G) theories enjoy a 2-group structure due to a non-trivial extension between a discrete 1-form symmetry and a continuous 0-form symmetry, emphasizing the dynamical consequences that a 2-group structure entails, and the family of AD theories that have it.
If time permits it, I will show that it is possible to obtain an infinite family of AD theories starting from an arbitrary D_p(G) theory, where the theories in the same family share some properties. We called this "bootstrapping" of D_p(G) theories. The bootstrapping is also visible at the level of the 3d mirror theories of the D_p(G).
My results are based mainly on arXiv:2203.16550 [hep-th] and arXiv:2208.11130 [hep-th].
Posted by: andrea
Thu
2 Feb 2023
Topological recursion, Airy structures, and its generalisations
Kento Osuga
(University of Tokyo)
Abstract:
Topological recursion has become known as a powerful recursive formalism to compute a variety of invariants in mathematics and physics. The list of applications includes matrix model correlation functions, 2d gravity amplitudes, topological string theory amplitudes, and more. Interestingly, recent study has shown that by introducing the notion of Airy structures, topological recursion can be described in terms of twisted representations of the Virasoro algebra. In this talk, I will first give an introductory overview of topological recursion as well as Airy structures. Then, I will present how one can generalise the current formalism of topological recursion, e.g. by upgrading the Virasoro algebra to the super Virasoro algebra or the q-Virasoro algebra. If time permits, I will also discuss expected applications of such generalisations. This is in part joint with Vincent Bouchard and also in part joint with Nitin Chidambaram.
Notice the unusual day!
Topological recursion has become known as a powerful recursive formalism to compute a variety of invariants in mathematics and physics. The list of applications includes matrix model correlation functions, 2d gravity amplitudes, topological string theory amplitudes, and more. Interestingly, recent study has shown that by introducing the notion of Airy structures, topological recursion can be described in terms of twisted representations of the Virasoro algebra. In this talk, I will first give an introductory overview of topological recursion as well as Airy structures. Then, I will present how one can generalise the current formalism of topological recursion, e.g. by upgrading the Virasoro algebra to the super Virasoro algebra or the q-Virasoro algebra. If time permits, I will also discuss expected applications of such generalisations. This is in part joint with Vincent Bouchard and also in part joint with Nitin Chidambaram.
Notice the unusual day!
Posted by: IC
January 2023
Mon
30 Jan 2023
LonTI: Introduction to CFT and Conformal Bootstrap
Andreas Stergiou
(King's College)
Abstract:
These lectures aim to provide a self-contained introduction to the modern conformal bootstrap method. The study of conformal field theory (CFT) will first be motivated and the รขโฌลoldรขโฌย way of studying CFTs as endpoints of RG flows will be explained. The set of ideas necessary to understand the conformal bootstrap method will then be introduced, and both analytic and numerical implementations of the conformal bootstrap method will be discussed.
These lectures aim to provide a self-contained introduction to the modern conformal bootstrap method. The study of conformal field theory (CFT) will first be motivated and the รขโฌลoldรขโฌย way of studying CFTs as endpoints of RG flows will be explained. The set of ideas necessary to understand the conformal bootstrap method will then be introduced, and both analytic and numerical implementations of the conformal bootstrap method will be discussed.
Posted by: CityU2
Mon
30 Jan 2023
LonTI Special Event: Careers in Quantitative Finance
Charles Martinez
(G-Research)
Abstract:
G-Research are a leading quantitative research and technology company based in London. Day to day we use a variety of quantitative techniques to predict financial markets from large data sets worldwide. Mathematics, statistics, machine learning, natural language processing and deep learning is what our business is built on. Our culture is academic and highly intellectual. In this seminar I will explain our background, current AI research applications to finance and our ongoing outreach and grants programme. The seminar will be aimed at PhD and Masters students who are curious about quant finance or interested in internship opportunities.
The presentation will be of a duration of 45 minutes with 15 minutes for Q&A.
We will cover the following topics:
Introducing G-Research
What happens in the black box?
What does a Quant look like?
Our recruitment and internship processes
Q&A
Bio: Dr Charles Martinez is the Academic Relations Manager at G-Research. Charles started his studies as a physicist at University Portsmouth Physics department's MPhys programme, and later completed a PhD in Phonon interactions in Gallium Nitride nanostructures at the University of Nottingham. Charles then worked on indexing and abstract databases at the Institution for Engineering and Technology (IET) before moving into sales in 2010. Charles' previous role was as Elsevier's Key Account Manager, managing sales and renewals for the UK Russell Group institutions, Government and Funding body accounts, including being one of the negotiators in the recent UK ScienceDirect Read and Publish agreement. Since leaving Elsevier Charles is dedicated to forming beneficial partnerships between G-Research and Europe's top institutions, and is living in Cambridge, UK. รขโฌโนรขโฌโน
G-Research are a leading quantitative research and technology company based in London. Day to day we use a variety of quantitative techniques to predict financial markets from large data sets worldwide. Mathematics, statistics, machine learning, natural language processing and deep learning is what our business is built on. Our culture is academic and highly intellectual. In this seminar I will explain our background, current AI research applications to finance and our ongoing outreach and grants programme. The seminar will be aimed at PhD and Masters students who are curious about quant finance or interested in internship opportunities.
The presentation will be of a duration of 45 minutes with 15 minutes for Q&A.
We will cover the following topics:
Introducing G-Research
What happens in the black box?
What does a Quant look like?
Our recruitment and internship processes
Q&A
Bio: Dr Charles Martinez is the Academic Relations Manager at G-Research. Charles started his studies as a physicist at University Portsmouth Physics department's MPhys programme, and later completed a PhD in Phonon interactions in Gallium Nitride nanostructures at the University of Nottingham. Charles then worked on indexing and abstract databases at the Institution for Engineering and Technology (IET) before moving into sales in 2010. Charles' previous role was as Elsevier's Key Account Manager, managing sales and renewals for the UK Russell Group institutions, Government and Funding body accounts, including being one of the negotiators in the recent UK ScienceDirect Read and Publish agreement. Since leaving Elsevier Charles is dedicated to forming beneficial partnerships between G-Research and Europe's top institutions, and is living in Cambridge, UK. รขโฌโนรขโฌโน
Posted by: CityU2
Wed
25 Jan 2023
Holographic duals to evaporating black holes
๐ London
Marija Tomasevic
(Ecole Polytechnique, CPHT)
Abstract:
We describe the dynamical evaporation of a black hole as the classical evolution in time of a black hole in an Anti-de Sitter braneworld. A bulk black hole whose horizon intersects the brane yields the classical bulk dual of a black hole coupled to quantum conformal fields. The evaporation of this black hole happens when the bulk horizon slides off the brane, making the horizon on the brane shrink. We use a large-D effective theory of the bulk Einstein equations to solve the time evolution of these systems. With this method, we study the dual evaporation of a variety of black holes interacting with colder radiation baths. We also obtain the dual of the collapse of holographic radiation to form a black hole on the brane.
We describe the dynamical evaporation of a black hole as the classical evolution in time of a black hole in an Anti-de Sitter braneworld. A bulk black hole whose horizon intersects the brane yields the classical bulk dual of a black hole coupled to quantum conformal fields. The evaporation of this black hole happens when the bulk horizon slides off the brane, making the horizon on the brane shrink. We use a large-D effective theory of the bulk Einstein equations to solve the time evolution of these systems. With this method, we study the dual evaporation of a variety of black holes interacting with colder radiation baths. We also obtain the dual of the collapse of holographic radiation to form a black hole on the brane.
Posted by: andrea
Wed
25 Jan 2023
AdS/CFT at loop order
Kostas Skenderis
(University of Southampton)
Abstract:
I will discuss how to setup renormalization of bulk loops in AdS and the implications for the AdS/CFT correspondence.
I will discuss how to setup renormalization of bulk loops in AdS and the implications for the AdS/CFT correspondence.
Posted by: IC2
Tue
24 Jan 2023
Uncovering the Structure of the epsilon-Expansion
Andreas Stergiou
(King's College London)
Abstract:
The epsilon-expansion was invented more than 50 years ago and has been used extensively ever since to study aspects of renormalization group flows and critical phenomena. Its most famous applications are found in theories involving scalar fields in (4-epsilon) dimensions. In this talk, we will discuss the structure of the epsilon-expansion and the fixed points that can be obtained within it. We will mostly focus on scalar theories, but we will also discuss theories with fermions as well as line defects. Our motivation is based on the goal of classifying conformal field theories in d=3 dimensions. We will describe recently discovered universal constraints obtained within the framework of the epsilon-expansion and show that a 'heavy handed' quest for fixed points yields a plethora of new ones. These fixed points reveal aspects of the structure of the epsilon-expansion and suggest that a classification of conformal field theories in d=3 is likely to be highly non-trivial.
The epsilon-expansion was invented more than 50 years ago and has been used extensively ever since to study aspects of renormalization group flows and critical phenomena. Its most famous applications are found in theories involving scalar fields in (4-epsilon) dimensions. In this talk, we will discuss the structure of the epsilon-expansion and the fixed points that can be obtained within it. We will mostly focus on scalar theories, but we will also discuss theories with fermions as well as line defects. Our motivation is based on the goal of classifying conformal field theories in d=3 dimensions. We will describe recently discovered universal constraints obtained within the framework of the epsilon-expansion and show that a 'heavy handed' quest for fixed points yields a plethora of new ones. These fixed points reveal aspects of the structure of the epsilon-expansion and suggest that a classification of conformal field theories in d=3 is likely to be highly non-trivial.
Posted by: IC
Thu
19 Jan 2023
Chiral Approach to Massive Higher Spins
๐ London
Alexander Ochirov
(University of Oxford and London Institute for Mathematical Sciences)
Abstract:
Quantum field theory of higher-spin particles is a formidable subject, where preserving the physical number of degrees of freedom in the Lorentz-invariant way requires a host of auxiliary fields. They can be chosen to have a rich gauge-symmetry structure, but introducing consistent interactions in such approaches is still a non-trivial task, with massive higher-spin Lagrangians specified only up to three points. In this talk, I will discuss a new, chiral description for massive higher-spin particles, which in four spacetime dimensions allows to do away with the unphysical degrees of freedom. This greatly facilitates the introduction of consistent interactions. I will concentrate on three theories, in which higher-spin matter is coupled to electrodynamics, non-Abelian gauge theory or gravity. These theories are currently the only examples of consistently interacting field theories with massive higher-spin fields.
Quantum field theory of higher-spin particles is a formidable subject, where preserving the physical number of degrees of freedom in the Lorentz-invariant way requires a host of auxiliary fields. They can be chosen to have a rich gauge-symmetry structure, but introducing consistent interactions in such approaches is still a non-trivial task, with massive higher-spin Lagrangians specified only up to three points. In this talk, I will discuss a new, chiral description for massive higher-spin particles, which in four spacetime dimensions allows to do away with the unphysical degrees of freedom. This greatly facilitates the introduction of consistent interactions. I will concentrate on three theories, in which higher-spin matter is coupled to electrodynamics, non-Abelian gauge theory or gravity. These theories are currently the only examples of consistently interacting field theories with massive higher-spin fields.
Posted by: QMW
Wed
18 Jan 2023
Spin chains for 4D N=2 SCFTs
๐ London
Elli Pomoni
(DESY)
Abstract:
In this talk, we will give an overview of the recent developments on the spin chains encoding the spectral problem of four dimensional N=2 superconformal gauge theories.
In this talk, we will give an overview of the recent developments on the spin chains encoding the spectral problem of four dimensional N=2 superconformal gauge theories.
Posted by: andrea
Wed
18 Jan 2023
Celestial chiral algebras, colour-kinematics duality and integrability
Ricardo Monteiro
(Queen Mary University of London)
Abstract:
We will discuss a connection between OPE algebras appearing in celestial holography for various theories and the `colour-kinematics duality' in the bulk spacetime description of those theories. Both the celestial algebras and the colour-kinematics duality take a particularly simple form for self-dual Yang-Mills and gravity. In particular, we show that the \(Lw_{1+\infty}\) celestial algebra recently unveiled in self-dual gravity arises from the soft expansion of an area-preserving diffeomorphism algebra, which plays the role of the kinematic algebra in the colour-kinematics duality. We also present deformations of the celestial algebras resulting from Moyal deformations of the self-dual theories, e.g. the deformation of \(Lw_{1+\infty}\) into \(LW_{1+\infty}\) in the case of self-dual gravity. In addition, we discuss the relation of these deformations to higher-spin theories of massless particles that can be thought of as extensions of self-dual Yang-Mills and gravity. Finally, we present a proof that tree-level scattering amplitudes in the theories we focus on vanish, signalling their classical integrability, which is an S-matrix version of the Ward conjecture for integrable systems.
We will discuss a connection between OPE algebras appearing in celestial holography for various theories and the `colour-kinematics duality' in the bulk spacetime description of those theories. Both the celestial algebras and the colour-kinematics duality take a particularly simple form for self-dual Yang-Mills and gravity. In particular, we show that the \(Lw_{1+\infty}\) celestial algebra recently unveiled in self-dual gravity arises from the soft expansion of an area-preserving diffeomorphism algebra, which plays the role of the kinematic algebra in the colour-kinematics duality. We also present deformations of the celestial algebras resulting from Moyal deformations of the self-dual theories, e.g. the deformation of \(Lw_{1+\infty}\) into \(LW_{1+\infty}\) in the case of self-dual gravity. In addition, we discuss the relation of these deformations to higher-spin theories of massless particles that can be thought of as extensions of self-dual Yang-Mills and gravity. Finally, we present a proof that tree-level scattering amplitudes in the theories we focus on vanish, signalling their classical integrability, which is an S-matrix version of the Ward conjecture for integrable systems.
Posted by: IC2
Tue
17 Jan 2023
Bootstrapping the 6D (2,0) theory with Reinforcement Learning
Costis Papageorgakis
(Queen Mary University of London)
Abstract:
I will describe a method for approximately solving the crossing equations in a general CFT, using Reinforcement Learning as a stochastic optimiser. I will then present an application of this approach in the context of the 6D (2,0) theory.
I will describe a method for approximately solving the crossing equations in a general CFT, using Reinforcement Learning as a stochastic optimiser. I will then present an application of this approach in the context of the 6D (2,0) theory.
Posted by: IC
Thu
12 Jan 2023
Classical Gravitational Observables from the Eikonal Operator
๐ London
Carlo Heissenberg
(Uppsala University and Nordita)
Abstract:
The eikonal exponentiation provides a way to obtain the classical limit of gravity amplitudes and to calculate the total deflection in collisions of compact objects in the Post-Minkowskian (PM) regime. In this talk I will illustrate how the eikonal phase can be promoted to an operator combining elastic and inelastic amplitudes in order to account for gravitational-wave emissions. Up to 3PM order, this restores manifest unitarity and allows us to calculate the linear and angular momentum of the gravitational field after the collision, as well as the changes in the linear and angular momenta of the colliding bodies. In this way, one can explicitly check the corresponding balance laws. I will also explain how the framework easily accommodates both radiative effects, static effects, and linear tidal corrections.
The eikonal exponentiation provides a way to obtain the classical limit of gravity amplitudes and to calculate the total deflection in collisions of compact objects in the Post-Minkowskian (PM) regime. In this talk I will illustrate how the eikonal phase can be promoted to an operator combining elastic and inelastic amplitudes in order to account for gravitational-wave emissions. Up to 3PM order, this restores manifest unitarity and allows us to calculate the linear and angular momentum of the gravitational field after the collision, as well as the changes in the linear and angular momenta of the colliding bodies. In this way, one can explicitly check the corresponding balance laws. I will also explain how the framework easily accommodates both radiative effects, static effects, and linear tidal corrections.
Posted by: QMW