Triangle Seminars
June 2024
Wed
26 Jun 2024
Irreversibility, QNEC and defects
📍 London
Ignacio S. Landea
(IFLP)
Abstract:
We use a relative entropy in order to establish the irreversibility of renormalization group flows on planar d-dimensional defects, embedded in D-dimensional conformal field theories. This proof completes and unifies all known defect irreversibility theorems for defect dimensions d≤ 4. The F-theorem on defects (d= 3) is a new result using information-theoretic methods.
We use a relative entropy in order to establish the irreversibility of renormalization group flows on planar d-dimensional defects, embedded in D-dimensional conformal field theories. This proof completes and unifies all known defect irreversibility theorems for defect dimensions d≤ 4. The F-theorem on defects (d= 3) is a new result using information-theoretic methods.
Posted by: andrea
Thu
20 Jun 2024
Interacting duality-invariant theories in diverse dimensions: new results
Sergei Kuzenko
(The University of Western Australia)
Abstract:
This talk will review recent results on the construction of U(1) duality-invariant nonlinear models for gauge (2n-1)-forms in d = 4n dimensions, including \(T \bar T\)-like flows in the space of such theories. In the four-dimensional case, we will briefly discuss the following U(1) duality-invariant nonlinear systems: (i) models for N-extended superconformal higher-spin multiplets; (ii) the low-energy effective action for N = 4 SYM on its Coulomb branch; and (iii) models for spontaneously broken local N=1 supersymmetry. If time permits, a new formulation for a self-interacting chiral gauge 2n-form in d = 4n + 2 dimensions will be discussed.
This talk will review recent results on the construction of U(1) duality-invariant nonlinear models for gauge (2n-1)-forms in d = 4n dimensions, including \(T \bar T\)-like flows in the space of such theories. In the four-dimensional case, we will briefly discuss the following U(1) duality-invariant nonlinear systems: (i) models for N-extended superconformal higher-spin multiplets; (ii) the low-energy effective action for N = 4 SYM on its Coulomb branch; and (iii) models for spontaneously broken local N=1 supersymmetry. If time permits, a new formulation for a self-interacting chiral gauge 2n-form in d = 4n + 2 dimensions will be discussed.
Posted by: QMW
Wed
19 Jun 2024
Fermion-Monopole Scattering in the Standard Model
Rishi Mouland
(Cambridge)
Abstract:
It’s been known since the work of Callan and Rubakov that a generic gauge theory harbours a riddle: the scattering of light fermions off heavy magnetic monopoles necessitates exotic outgoing states, seemingly with fractional occupation numbers. I will first explain how we can make sense of these outgoing states in the modern language of generalised symmetries: They are created by operators living at the edge of a topological surface, and in turn correspond to states in a particular twisted Hilbert space. I will then apply this general formalism to the original case of interest, the Standard Model itself, where the resulting states turn out to carry fractionalised baryon and lepton numbers. I will finally discuss various other scenarios, including some that require non-invertible symmetry defects.
It’s been known since the work of Callan and Rubakov that a generic gauge theory harbours a riddle: the scattering of light fermions off heavy magnetic monopoles necessitates exotic outgoing states, seemingly with fractional occupation numbers. I will first explain how we can make sense of these outgoing states in the modern language of generalised symmetries: They are created by operators living at the edge of a topological surface, and in turn correspond to states in a particular twisted Hilbert space. I will then apply this general formalism to the original case of interest, the Standard Model itself, where the resulting states turn out to carry fractionalised baryon and lepton numbers. I will finally discuss various other scenarios, including some that require non-invertible symmetry defects.
Posted by: QMW
Wed
12 Jun 2024
Hidden Unitarity in the SCFT/VOA Correspondence
Christopher Beem
(Oxford)
Abstract:
Four-dimensional N=2 superconformal field theories give rise, via a cohomological construction that I will review, to associated vertex operator algebras that have been much investigated in the last decade. A curiosity of this construction is that for unitary parent SCFT, the vertex operator algebras so-realised are non-unitary. In this talk I will present the structure on these VOAs that encodes unitarity of the parent theory. Like conventional unitarity, this hidden unitarity imposes strong constraints. I will describe efforts to impose this constraint for Virasoro VOAs (and possibly affine Kac–Moody vertex algebras) leading to (conjectural) classification results for central charges/levels at which these algebras are compatible with four-dimensional unitarity. The talk is based on work in progress with A. Ardehali, M. Lemos, and L. Rastelli.
Four-dimensional N=2 superconformal field theories give rise, via a cohomological construction that I will review, to associated vertex operator algebras that have been much investigated in the last decade. A curiosity of this construction is that for unitary parent SCFT, the vertex operator algebras so-realised are non-unitary. In this talk I will present the structure on these VOAs that encodes unitarity of the parent theory. Like conventional unitarity, this hidden unitarity imposes strong constraints. I will describe efforts to impose this constraint for Virasoro VOAs (and possibly affine Kac–Moody vertex algebras) leading to (conjectural) classification results for central charges/levels at which these algebras are compatible with four-dimensional unitarity. The talk is based on work in progress with A. Ardehali, M. Lemos, and L. Rastelli.
Posted by: QMW
Thu
6 Jun 2024
Pedagogical Introduction to Geometric Langlands and its Generalizations via Gauge and String Theory, 4 of 4
Mengchwan Tan
(NUS, Singapore)
Abstract:
TITLE:
The AGT Duality and Beilinson-Drinfeld's Original Formulation of Geometric Langlands Duality via CFT
ABS:
The original mathematical formulation of geometric Langlands duality by Beilinson-Drinfeld involved CFT, not gauge theory. It was therefore an outstanding question how Kapustin-Witten's gauge-theoretic approach is related to Beilinson-Drinfeld's CFT approach. We will shed light on this question via string/M-theory. In particular, we first consider a modification of our physical setup manifesting the Braverman-Finkelberg geometric Langlands duality to arrive at an AGT duality which relates gauge theory to affine W-algebras. Then, it can be explained that the KW and BD formulations are just string-dual to each other.
TITLE:
The AGT Duality and Beilinson-Drinfeld's Original Formulation of Geometric Langlands Duality via CFT
ABS:
The original mathematical formulation of geometric Langlands duality by Beilinson-Drinfeld involved CFT, not gauge theory. It was therefore an outstanding question how Kapustin-Witten's gauge-theoretic approach is related to Beilinson-Drinfeld's CFT approach. We will shed light on this question via string/M-theory. In particular, we first consider a modification of our physical setup manifesting the Braverman-Finkelberg geometric Langlands duality to arrive at an AGT duality which relates gauge theory to affine W-algebras. Then, it can be explained that the KW and BD formulations are just string-dual to each other.
Posted by: oxford
Wed
5 Jun 2024
Pedagogical Introduction to Geometric Langlands and its Generalizations via Gauge and String Theory, 3 of 4
Mengchwan Tan
(NUS, Singapore)
Abstract:
TITLE:
Braverman-Finkelberg Generalization of Geometric Langlands Duality in String Theory
ABS:
Braverman-Finkelberg considered a generalization of the geometric Satake isomorphism to involve not Lie but Kac-Moody groups, and in so doing, arrived at a formulation of geometric Langlands duality which involves not complex curves, but complex surfaces. Specifically, the formulation relates the intersection cohomology of the moduli space of G-instantons on orbifold complex surfaces, to modules of a Langlands-dual affine Lie algebra with level determined by the order of the singularity. We will furnish a string/M-theoretic derivation of their mathematical conjecture.
TITLE:
Braverman-Finkelberg Generalization of Geometric Langlands Duality in String Theory
ABS:
Braverman-Finkelberg considered a generalization of the geometric Satake isomorphism to involve not Lie but Kac-Moody groups, and in so doing, arrived at a formulation of geometric Langlands duality which involves not complex curves, but complex surfaces. Specifically, the formulation relates the intersection cohomology of the moduli space of G-instantons on orbifold complex surfaces, to modules of a Langlands-dual affine Lie algebra with level determined by the order of the singularity. We will furnish a string/M-theoretic derivation of their mathematical conjecture.
Posted by: oxford
Wed
5 Jun 2024
Bootstrapping F-theory
Shai Chester
(IC)
Abstract:
We consider type IIB string theory with \(N\) D3 branes and various configurations of sevenbranes, such that the string coupling \(g_s\) is fixed to a constant finite value. These are the simplest realizations of F-theory, and are holographically dual either to a to a rank \(N\) gauge for any coupling tau, or to non-Lagrangian CFTs such as Argyres-Douglas and Minahan-Nemeschansky theory. We compute the mass deformed sphere free energy F(m) using localization in the case of the Lagrangian theory, and the Seiberg-Witten curve for the non-Lagrangian theories. We show how F(m) can be used along with the analytic bootstrap to fix the large N expansion of flavor multiplet correlators in these CFTs, which are dual to scattering of gluons on AdS_5 x S^3, and in the flat space limit determine the effective theory of sevenbranes in F-theory. In particular, we compute the log threshold terms for all the theories and the first higher derivative correction F^4 for the Lagrangian theory for finite tau, and find a precise match in the flat space limit in all cases. Finally, we use numerical bootstrap to study the Lagrangian theory at finite N and tau.
We consider type IIB string theory with \(N\) D3 branes and various configurations of sevenbranes, such that the string coupling \(g_s\) is fixed to a constant finite value. These are the simplest realizations of F-theory, and are holographically dual either to a to a rank \(N\) gauge for any coupling tau, or to non-Lagrangian CFTs such as Argyres-Douglas and Minahan-Nemeschansky theory. We compute the mass deformed sphere free energy F(m) using localization in the case of the Lagrangian theory, and the Seiberg-Witten curve for the non-Lagrangian theories. We show how F(m) can be used along with the analytic bootstrap to fix the large N expansion of flavor multiplet correlators in these CFTs, which are dual to scattering of gluons on AdS_5 x S^3, and in the flat space limit determine the effective theory of sevenbranes in F-theory. In particular, we compute the log threshold terms for all the theories and the first higher derivative correction F^4 for the Lagrangian theory for finite tau, and find a precise match in the flat space limit in all cases. Finally, we use numerical bootstrap to study the Lagrangian theory at finite N and tau.
Posted by: IC2
Tue
4 Jun 2024
Pedagogical Introduction to Geometric Langlands and its Generalizations via Gauge and String Theory, 2 of 4
Mengchwan Tan
(NUS, Singapore)
Abstract:
TITLE:
An introduction to Geometric Langlands Duality: from Faraday to Montonen-Olive to Hitchin to Kapustin-Witten
ABS:
As the first two of a four-part Bragg Lecture Series, we will furnish a pedestrian introduction to geometric Langlands duality via its manifestation in physical gauge theory. To this end, we will first explain what the arithmetic Langlands duality is, and its geometric version. Then, we will cover the underlying physics and math ideas starting with Faraday and electromagnetism, on to Montonen-Olive and the Langlands duality of electric-magnetic charges, then to Hitchin and the mirror symmetry of his moduli spaces, and finally, to Kapustin-Witten and S-duality of 4d N=4 topological gauge theory.
TITLE:
An introduction to Geometric Langlands Duality: from Faraday to Montonen-Olive to Hitchin to Kapustin-Witten
ABS:
As the first two of a four-part Bragg Lecture Series, we will furnish a pedestrian introduction to geometric Langlands duality via its manifestation in physical gauge theory. To this end, we will first explain what the arithmetic Langlands duality is, and its geometric version. Then, we will cover the underlying physics and math ideas starting with Faraday and electromagnetism, on to Montonen-Olive and the Langlands duality of electric-magnetic charges, then to Hitchin and the mirror symmetry of his moduli spaces, and finally, to Kapustin-Witten and S-duality of 4d N=4 topological gauge theory.
Posted by: oxford
Mon
3 Jun 2024
Pedagogical Introduction to Geometric Langlands and its Generalizations via Gauge and String Theory, 1 of 4
Mengchwan Tan
(NUS, Singapore)
Abstract:
TITLE:
An introduction to Geometric Langlands Duality: from Faraday to Montonen-Olive to Hitchin to Kapustin-Witten
ABS:
As the first two of a four-part Bragg Lecture Series, we will furnish a pedestrian introduction to geometric Langlands duality via its manifestation in physical gauge theory. To this end, we will first explain what the arithmetic Langlands duality is, and its geometric version. Then, we will cover the underlying physics and math ideas starting with Faraday and electromagnetism, on to Montonen-Olive and the Langlands duality of electric-magnetic charges, then to Hitchin and the mirror symmetry of his moduli spaces, and finally, to Kapustin-Witten and S-duality of 4d N=4 topological gauge theory.
TITLE:
An introduction to Geometric Langlands Duality: from Faraday to Montonen-Olive to Hitchin to Kapustin-Witten
ABS:
As the first two of a four-part Bragg Lecture Series, we will furnish a pedestrian introduction to geometric Langlands duality via its manifestation in physical gauge theory. To this end, we will first explain what the arithmetic Langlands duality is, and its geometric version. Then, we will cover the underlying physics and math ideas starting with Faraday and electromagnetism, on to Montonen-Olive and the Langlands duality of electric-magnetic charges, then to Hitchin and the mirror symmetry of his moduli spaces, and finally, to Kapustin-Witten and S-duality of 4d N=4 topological gauge theory.
Posted by: oxford
May 2024
Wed
29 May 2024
Subleading structure of asymptotically-flat spacetimes
Marc Geiller
(ENS Lyon)
Abstract:
Asymptotically-flat spacetimes play a central role in the study of gravitational radiation. They are also the arena which enables to understand the relationship between asymptotic symmetries, soft graviton theorems, and memory effects. While this relationship is well understood at leading order in terms of BMS symmetries and flux-balance laws for the mass and angular momentum, the subleading structure has only begun to be investigated recently. In this talk we will present a study of this subleading structure using the Newman-Penrose formalism. This enables to identify an infinite tower of quasi-conserved charges generating an intriguing algebraic structure.
Asymptotically-flat spacetimes play a central role in the study of gravitational radiation. They are also the arena which enables to understand the relationship between asymptotic symmetries, soft graviton theorems, and memory effects. While this relationship is well understood at leading order in terms of BMS symmetries and flux-balance laws for the mass and angular momentum, the subleading structure has only begun to be investigated recently. In this talk we will present a study of this subleading structure using the Newman-Penrose formalism. This enables to identify an infinite tower of quasi-conserved charges generating an intriguing algebraic structure.
Posted by: andrea
Wed
29 May 2024
Holography at finite N for N=4 SYM and S-folds
Jesse van Muiden
(SISSA)
Abstract:
Recent progress has provided methods to compute and match finite N (supersymmetric) partition functions on both sides of the holographic duality within string and M-theory. An advent that allows for interesting opportunities in the study of quantized strings and branes in curved backgrounds. I will discuss \mathcal{N}=4 SYM, its S-fold cousins, and how localization allows to compute their supersymmetric partition functions analytically as a function of N. We will subsequently discuss some peculiar features of these S-folds; such as their seemingly non-compact conformal manifold, and the fact that their partition functions can be expanded in fluctuating gravitons and D3-branes, very much a-like the giant graviton expansion in \mathcal{N}=4 SYM, even though a clear index interpretation is absent on the QFT side.
Recent progress has provided methods to compute and match finite N (supersymmetric) partition functions on both sides of the holographic duality within string and M-theory. An advent that allows for interesting opportunities in the study of quantized strings and branes in curved backgrounds. I will discuss \mathcal{N}=4 SYM, its S-fold cousins, and how localization allows to compute their supersymmetric partition functions analytically as a function of N. We will subsequently discuss some peculiar features of these S-folds; such as their seemingly non-compact conformal manifold, and the fact that their partition functions can be expanded in fluctuating gravitons and D3-branes, very much a-like the giant graviton expansion in \mathcal{N}=4 SYM, even though a clear index interpretation is absent on the QFT side.
Posted by: QMW
Tue
28 May 2024
On the IR divergences in de Sitter. loops, resummation and the semi-classical wavefunction
Sebastian Cespedes
(Imperial College London)
Abstract:
Detecting local Non-Gaussianity provides valuable insights into the early universe's particle composition. Interactions between the inflaton and light particles yield distinctive signatures, potentially observable in upcoming surveys. However, addressing IR divergences in light fields on de Sitter spacetimes requires careful treatment. Stochastic inflation offers a solution, but its relationship with perturbative computations remains unclear. In this presentation, we establish a precise connection between perturbation theory and stochastic formalism using the wavefunction formalism. We extend this analysis to multifield inflation models and clarify recent non-perturbative findings from stochastic inflation through their compatibility with perturbation theory calculations.
Detecting local Non-Gaussianity provides valuable insights into the early universe's particle composition. Interactions between the inflaton and light particles yield distinctive signatures, potentially observable in upcoming surveys. However, addressing IR divergences in light fields on de Sitter spacetimes requires careful treatment. Stochastic inflation offers a solution, but its relationship with perturbative computations remains unclear. In this presentation, we establish a precise connection between perturbation theory and stochastic formalism using the wavefunction formalism. We extend this analysis to multifield inflation models and clarify recent non-perturbative findings from stochastic inflation through their compatibility with perturbation theory calculations.
Posted by: IC2
Tue
28 May 2024
Microstates of Accelerating and Supersymmetric AdS(4) Black Holes from the Spindle Index
Seyedmorteza Hosseini
(Imperial College London)
Abstract:
I will present a method for deriving the microscopic entropy of a very general class of supersymmetric, rotating, and accelerating black holes in AdS(4). This is achieved by analyzing the large-N limit of the spindle index.
I will present a method for deriving the microscopic entropy of a very general class of supersymmetric, rotating, and accelerating black holes in AdS(4). This is achieved by analyzing the large-N limit of the spindle index.
Posted by: IC2
Tue
28 May 2024
Generalized symmetries and duality in lattice models using tensor networks
📍 London
Laurens Lootens
(Cambridge)
Abstract:
In recent years, there has been a lot of interest in a generalized notion of symmetry, obtained by relaxing the invertibility constraint and/or allowing symmetry operators to act on submanifolds rather than the full space. The mathematical structure underlying these generalized symmetries is provided by (higher) category theory, but it turns out that in the lattice setting, the abstract categorical formulation can be broken down to concrete tensor network operators that realize these generalized symmetries. In a certain sense, these tensor network operators provide the lattice representation theory of these generalized symmetries. As an application, I will explain how this representation theory provides a systematic, constructive theory for duality transformations on the lattice. Additionally, I will explain how dualities and generalized symmetries can be turned into unitary operators by including an ancillary degree of freedom, turning them into completely positive maps.
In recent years, there has been a lot of interest in a generalized notion of symmetry, obtained by relaxing the invertibility constraint and/or allowing symmetry operators to act on submanifolds rather than the full space. The mathematical structure underlying these generalized symmetries is provided by (higher) category theory, but it turns out that in the lattice setting, the abstract categorical formulation can be broken down to concrete tensor network operators that realize these generalized symmetries. In a certain sense, these tensor network operators provide the lattice representation theory of these generalized symmetries. As an application, I will explain how this representation theory provides a systematic, constructive theory for duality transformations on the lattice. Additionally, I will explain how dualities and generalized symmetries can be turned into unitary operators by including an ancillary degree of freedom, turning them into completely positive maps.
Posted by: QMW
Thu
23 May 2024
Tracy-Widom distribution in supersymmetric gauge theories
📍 London
Gregory Korchemsky
(IPhT Saclay)
Abstract:
It has recently been recognized that various observables in different four-dimensional supersymmetric gauge theories can be computed for an arbitrary 't Hooft coupling as determinants of certain semi-infinite matrices. It turns out that these quantities can be expressed as Fredholm determinants of the so-called Bessel kernel and they are closely related to celebrated Tracy-Widom distribution (more precisely, its finite temperature generalization) describing level-spacing distributions in matrix models. We exploit this relation to determine their dependence on the ’t Hooft coupling constant. Unlike the weak coupling expansion, which has a finite radius of convergence, the strong coupling expansion is factorially divergent, necessitating the inclusion of nonperturbative, exponentially small corrections. We develop a method to systematically compute these corrections and discuss the resurgent properties of the resulting transseries.
It has recently been recognized that various observables in different four-dimensional supersymmetric gauge theories can be computed for an arbitrary 't Hooft coupling as determinants of certain semi-infinite matrices. It turns out that these quantities can be expressed as Fredholm determinants of the so-called Bessel kernel and they are closely related to celebrated Tracy-Widom distribution (more precisely, its finite temperature generalization) describing level-spacing distributions in matrix models. We exploit this relation to determine their dependence on the ’t Hooft coupling constant. Unlike the weak coupling expansion, which has a finite radius of convergence, the strong coupling expansion is factorially divergent, necessitating the inclusion of nonperturbative, exponentially small corrections. We develop a method to systematically compute these corrections and discuss the resurgent properties of the resulting transseries.
Posted by: QMW
Wed
22 May 2024
Modular Hamiltonians, relative entropy and the entropy-area law in de Sitter spacetime
📍 London
Markus Froeb
(U. Leipzig)
Abstract:
In a very general setting, entropy quantifies the amount of
information about a system that an observer has access to. However, in contrast to quantum mechanics, in quantum field theory naive measures of entropy are divergent. To obtain finite results, one needs to consider measures such as relative entropy, which can be computed from the modular Hamiltonian using Tomita–Takesaki theory.
In this talk, I will give a short introduction to Tomita–Takesaki modular theory and present examples of modular Hamiltonians. Using these, I will give results for therelative entropy between the de Sitter vacuum state and a coherent excitation thereof in diamond and wedge regions, and show explicitly that the result satisfies the expected properties for a relative entropy. Finally, I will use local thermodynamic laws to determine the local temperature that is measured by an observer, and consider the backreaction of the quantum state on the geometry to prove an entropy-area law for de Sitter spacetime.
Based on arXiv:arXiv:2308.14797, 2310.12185, 2311.13990 and 2312.04629.
In a very general setting, entropy quantifies the amount of
information about a system that an observer has access to. However, in contrast to quantum mechanics, in quantum field theory naive measures of entropy are divergent. To obtain finite results, one needs to consider measures such as relative entropy, which can be computed from the modular Hamiltonian using Tomita–Takesaki theory.
In this talk, I will give a short introduction to Tomita–Takesaki modular theory and present examples of modular Hamiltonians. Using these, I will give results for therelative entropy between the de Sitter vacuum state and a coherent excitation thereof in diamond and wedge regions, and show explicitly that the result satisfies the expected properties for a relative entropy. Finally, I will use local thermodynamic laws to determine the local temperature that is measured by an observer, and consider the backreaction of the quantum state on the geometry to prove an entropy-area law for de Sitter spacetime.
Based on arXiv:arXiv:2308.14797, 2310.12185, 2311.13990 and 2312.04629.
Posted by: andrea
Wed
22 May 2024
3d Topological Orders Labeled by Seifert Manifolds
Federico Bonetti
(Durham)
Abstract:
Topological orders in 2+1 dimensions are captured by modular tensor categories (MTCs). We propose a correspondence that assigns a fusion category to a pair (M,G), where M is a Seifert 3-manifold and G is an ADE Lie group. We conjecture that the fusion category associated to (M,G) is an MTC if and only if M has trivial first homology group with coefficients in the center of G. The construction determines the spins of anyons and their S-matrix, and provides a constructive way to access the R- and F-symbols from simple building blocks. We explore the possibility that this correspondence provides an alternative classification of MTCs, which is put to the test by realizing all MTCs (unitary or non-unitary) with rank at most 5.
Topological orders in 2+1 dimensions are captured by modular tensor categories (MTCs). We propose a correspondence that assigns a fusion category to a pair (M,G), where M is a Seifert 3-manifold and G is an ADE Lie group. We conjecture that the fusion category associated to (M,G) is an MTC if and only if M has trivial first homology group with coefficients in the center of G. The construction determines the spins of anyons and their S-matrix, and provides a constructive way to access the R- and F-symbols from simple building blocks. We explore the possibility that this correspondence provides an alternative classification of MTCs, which is put to the test by realizing all MTCs (unitary or non-unitary) with rank at most 5.
Posted by: QMW
Tue
21 May 2024
Localization in supergravity
James Sparks
(University of Oxford)
Abstract:
We describe a powerful new technique for computing various physical observables in supergravity, without solving any supergravity equations. Applications include gravitational free energies, black hole entropies, and central charges and other CFT quantities of interest in holography. In the talk I will aim to describe the general idea, and give a flavour of some applications.
We describe a powerful new technique for computing various physical observables in supergravity, without solving any supergravity equations. Applications include gravitational free energies, black hole entropies, and central charges and other CFT quantities of interest in holography. In the talk I will aim to describe the general idea, and give a flavour of some applications.
Posted by: IC2
Tue
21 May 2024
Organising genius: scientific progress and global cooperation
Various Various
(Various)
Abstract:
We are hosting a half-day symposium for scientists, innovators and policymakers to debate the framework within which genius flourishes.
Speakers include Chinyelu Onwurah (Shadow Minister for Science), George Freeman (former Minister for Science), Sir Martyn Poliakoff (Faraday Medalist), et al
https://lims.ac.uk/event/organising-genius-scientific-progress-and-international-cooperation/
We are hosting a half-day symposium for scientists, innovators and policymakers to debate the framework within which genius flourishes.
Speakers include Chinyelu Onwurah (Shadow Minister for Science), George Freeman (former Minister for Science), Sir Martyn Poliakoff (Faraday Medalist), et al
https://lims.ac.uk/event/organising-genius-scientific-progress-and-international-cooperation/
Posted by: oxford
Thu
16 May 2024
Quantum entanglement and emergent geometry from matrix degrees of freedom
Masanori Hanada
(Queen Mary)
Abstract:
For matrix models and QFT, we discuss how holographic emergent geometry appears from matrix degrees of freedom (specifically, adjoint scalars in super Yang-Mills theory) and how operator algebra that describes an arbitrary region of the bulk geometry can be constructed. We pay attention to the subtle difference between the notions of wave packets that describe low-energy excitations: QFT wave packet associated with the spatial dimensions of QFT, matrix wave packet associated with the emergent dimensions from matrix degrees of freedom, and bulk wave packet which is a combination of QFT and matrix wave packets. In QFT, there is an intriguing interplay between QFT wave packet and matrix wave packet that connects quantum entanglement and emergent geometry. We propose that the bulk wave packet is the physical object in QFT that describes the emergent geometry from entanglement. This proposal sets a unified view on two seemingly different mechanisms of holographic emergent geometry: one based on matrix eigenvalues and the other based on quantum entanglement. Further intuition comes from the similarity to traversable wormholes.
For matrix models and QFT, we discuss how holographic emergent geometry appears from matrix degrees of freedom (specifically, adjoint scalars in super Yang-Mills theory) and how operator algebra that describes an arbitrary region of the bulk geometry can be constructed. We pay attention to the subtle difference between the notions of wave packets that describe low-energy excitations: QFT wave packet associated with the spatial dimensions of QFT, matrix wave packet associated with the emergent dimensions from matrix degrees of freedom, and bulk wave packet which is a combination of QFT and matrix wave packets. In QFT, there is an intriguing interplay between QFT wave packet and matrix wave packet that connects quantum entanglement and emergent geometry. We propose that the bulk wave packet is the physical object in QFT that describes the emergent geometry from entanglement. This proposal sets a unified view on two seemingly different mechanisms of holographic emergent geometry: one based on matrix eigenvalues and the other based on quantum entanglement. Further intuition comes from the similarity to traversable wormholes.
Posted by: oxford
Wed
15 May 2024
Radial canonical AdS_3 gravity and TTbar theory
📍 London
Nele Callebaut
(Cologne U.)
Abstract:
In this talk, I will employ an ADM deparametrization strategy to discuss the radial canonical formalism of asymptotically AdS_3 gravity. It leads to the identification of a radial 'time' before quantization, namely the volume time, which is canonically conjugate to York time. Holographically, this allows to interpret the semi-classical partition function of TTbar theory as a Schrodinger wavefunctional satisfying a Schrodinger evolution equation in volume time. The canonical perspective can be used to construct from the Hamilton-Jacobi equation the BTZ solution, and corresponding semi-classical Wheeler-DeWitt states. Based on upcoming work with Matthew J. Blacker, Blanca Hergueta and Sirui Ning.
In this talk, I will employ an ADM deparametrization strategy to discuss the radial canonical formalism of asymptotically AdS_3 gravity. It leads to the identification of a radial 'time' before quantization, namely the volume time, which is canonically conjugate to York time. Holographically, this allows to interpret the semi-classical partition function of TTbar theory as a Schrodinger wavefunctional satisfying a Schrodinger evolution equation in volume time. The canonical perspective can be used to construct from the Hamilton-Jacobi equation the BTZ solution, and corresponding semi-classical Wheeler-DeWitt states. Based on upcoming work with Matthew J. Blacker, Blanca Hergueta and Sirui Ning.
Posted by: andrea
Tue
14 May 2024
Primordial Non-Gaussianity: the fNL sim 1 threshold
Paolo Creminelli
(ICTP, Trieste)
Abstract:
I will review the theoretical and experimental status in the search of primordial non-Gaussianity, focussing on some recent developments and ideas.
In particular I will try to answer the question: what are we going to learn when experiments will be able to probe f_NL ~ 1?
I will review the theoretical and experimental status in the search of primordial non-Gaussianity, focussing on some recent developments and ideas.
In particular I will try to answer the question: what are we going to learn when experiments will be able to probe f_NL ~ 1?
Posted by: IC2
Wed
8 May 2024
Exponential networks for linear partitions
Johannes Walcher
(Heidelberg)
Abstract:
Previous work has given proof and evidence that BPS states in local Calabi-Yau 3-folds can be described and counted by exponential networks on the punctured plane, with the help of a suitable non-abelianization map to the mirror curve. This provides an appealing elementary depiction of moduli of special Lagrangian submanifolds, but so far only a handful of examples have been successfully worked out in detail. In this talk, I will present an explicit correspondence between torus fixed points of the Hilbert scheme of points on ℂ^2⊂ℂ^3 and anomaly free exponential networks attached to the quadratically framed pair of pants. This description realizes an interesting, and seemingly novel, “age decomposition†of linear partitions. We also provide further details about the networks’ perspective on the full D-brane moduli space.
Previous work has given proof and evidence that BPS states in local Calabi-Yau 3-folds can be described and counted by exponential networks on the punctured plane, with the help of a suitable non-abelianization map to the mirror curve. This provides an appealing elementary depiction of moduli of special Lagrangian submanifolds, but so far only a handful of examples have been successfully worked out in detail. In this talk, I will present an explicit correspondence between torus fixed points of the Hilbert scheme of points on ℂ^2⊂ℂ^3 and anomaly free exponential networks attached to the quadratically framed pair of pants. This description realizes an interesting, and seemingly novel, “age decomposition†of linear partitions. We also provide further details about the networks’ perspective on the full D-brane moduli space.
Posted by: IC2
Wed
8 May 2024
SU(N) Principal Chiral Model at large N
📍 London
Evgeny Sobko
(LIMS, London)
Abstract:
I will show how to calculate 1/N expansion of the vacuum energy of the 2D SU(N) Principal Chiral Model for a certain profile of chemical potentials. Combining this expansion with strong coupling I will identify double-scaling limit which bears striking similarities to the c = 1 non-critical string theory and suggests that the double-scaled PCM is dual to a non-critical string with a (2 + 1)-dimensional target space where an additional dimension emerges dynamically from the SU(N) Dynkin diagram. Developing this idea further, I will show how to solve large-N PCM for an arbitrary set of chemical potentials and any interaction strength, a unique result of such kind for an asymptotically free QFT. The solution matches one-loop perturbative calculation at weak coupling, and in the opposite strong-coupling regime exhibits an emergent spacial dimension from the continuum limit of the SU(N) Dynkin diagram. In the second part of my talk I will show that the calculation of the expectation value of half-BPS circular Wilson loops in N = 2 superconformal A_{n−1} quiver gauge theories trivialises in the large n limit (similarly to PCM), construct 1/n expansion, identify DS limit and solve it for any finite value of DS parameter and any profile of coupling constants.
I will show how to calculate 1/N expansion of the vacuum energy of the 2D SU(N) Principal Chiral Model for a certain profile of chemical potentials. Combining this expansion with strong coupling I will identify double-scaling limit which bears striking similarities to the c = 1 non-critical string theory and suggests that the double-scaled PCM is dual to a non-critical string with a (2 + 1)-dimensional target space where an additional dimension emerges dynamically from the SU(N) Dynkin diagram. Developing this idea further, I will show how to solve large-N PCM for an arbitrary set of chemical potentials and any interaction strength, a unique result of such kind for an asymptotically free QFT. The solution matches one-loop perturbative calculation at weak coupling, and in the opposite strong-coupling regime exhibits an emergent spacial dimension from the continuum limit of the SU(N) Dynkin diagram. In the second part of my talk I will show that the calculation of the expectation value of half-BPS circular Wilson loops in N = 2 superconformal A_{n−1} quiver gauge theories trivialises in the large n limit (similarly to PCM), construct 1/n expansion, identify DS limit and solve it for any finite value of DS parameter and any profile of coupling constants.
Posted by: andrea
Fri
3 May 2024
Classical Black Hole Scattering from a World-Line Quantum Field Theory
📍 London
Jan Plefka
(Humboldt U.)
Abstract:
Predicting the outcome of scattering processes of elementary particles in colliders is the central achievement of relativistic quantum field theory applied to the fundamental (non-gravitational) interactions of nature. While the gravitational interactions are too minuscule to be observed in the microcosm, they dominate the interactions at large scales. As such the inspiral and merger of black holes and neutron stars in our universe are now routinely observed by gravitational wave detectors. The need for high precision theory predictions of the emitted gravitational waveforms has opened a new window for the application of perturbative quantum field theory techniques to the domain of gravity. In this talk I will show how observables in the classical scattering of black holes and neutron stars can be efficiently computed in a perturbative expansion using a world-line quantum field theory; thereby combining state-of-the-art Feynman integration technology with perturbative quantum gravity. Here, the black holes or neutron stars are modelled as point particles in an effective field theory sense. Fascinatingly, the intrinsic spin of the black holes may be captured by a supersymmetric extension of the world-line theory, enabling the computation of the far field wave-form including spin and tidal effects to highest precision. I will review our most recent results at the fifth order in the post-Minkowskian expansion amounting to the computations of tens of thousands of four loop Feynman integrals.
Predicting the outcome of scattering processes of elementary particles in colliders is the central achievement of relativistic quantum field theory applied to the fundamental (non-gravitational) interactions of nature. While the gravitational interactions are too minuscule to be observed in the microcosm, they dominate the interactions at large scales. As such the inspiral and merger of black holes and neutron stars in our universe are now routinely observed by gravitational wave detectors. The need for high precision theory predictions of the emitted gravitational waveforms has opened a new window for the application of perturbative quantum field theory techniques to the domain of gravity. In this talk I will show how observables in the classical scattering of black holes and neutron stars can be efficiently computed in a perturbative expansion using a world-line quantum field theory; thereby combining state-of-the-art Feynman integration technology with perturbative quantum gravity. Here, the black holes or neutron stars are modelled as point particles in an effective field theory sense. Fascinatingly, the intrinsic spin of the black holes may be captured by a supersymmetric extension of the world-line theory, enabling the computation of the far field wave-form including spin and tidal effects to highest precision. I will review our most recent results at the fifth order in the post-Minkowskian expansion amounting to the computations of tens of thousands of four loop Feynman integrals.
Posted by: QMW
Wed
1 May 2024
TBA
Ning Su
(MIT/Caltech)
Wed
1 May 2024
Classical observables of General Relativity from scattering amplitudes
📍 London
Paolo di Vecchia
(Stockholm U. and Nordita)
Abstract:
I will be using scattering amplitudes, instead of the Lagrangian of General Relativity (GR), to compute classical observables in GR. In the first part of the seminar I will consider the elastic scattering of two massive particles, describing two black holes, and I will show how to compute the eikonal up to two-loop order, corresponding to third Post-Minkowskian (3PM) order, that contains all the classical information. From it I will compute the first observable that is the classical deflection angle. In the second part of the seminar I will consider inelastic processes with the emission of soft gravitons. In this case the eikonal becomes an operator containing the creation and annihilation operators of the gravitons. The case of soft gravitons can be treated following the Bloch-Nordsieck approach and, in this case, I will be computing two other observables: the zero-frequency limit (ZFL) of the spectrum dE/d\omega of the emitted radiation and the angular momentum loss at 2PM and 3PM. I will consider also the case in which there are static modes localised at \(\omega=0\). In the third part of the seminar I will be discussing soft theorems with one graviton emission, first briefly at tree level, and then at loop level following the paper by Weinberg from 1965. Assuming the eikonal resummation and that all infrared divergences in the case of gravity come only from one loop diagrams, I will compute the universal soft terms, corresponding to \(\frac{1}{\omega}\), \(\log \omega\) and \(\omega \log^2 \omega\), first at the tree and one-loop level and then for the last two observables also at two-loop level. I will then use them to compute their contribution to the spectrum of emitted energy. Finally, if I have time left, I I will study the high energy limit. In particular, since the graviton is the massless particle with the highest spin, we expect universality at high energy. I will show that universality at high energy is satisfied both in the elastic and inelastic case, but this happens in the inelastic case in a very non trivial way. I will end with some conclusions and with a list of open problems.
I will be using scattering amplitudes, instead of the Lagrangian of General Relativity (GR), to compute classical observables in GR. In the first part of the seminar I will consider the elastic scattering of two massive particles, describing two black holes, and I will show how to compute the eikonal up to two-loop order, corresponding to third Post-Minkowskian (3PM) order, that contains all the classical information. From it I will compute the first observable that is the classical deflection angle. In the second part of the seminar I will consider inelastic processes with the emission of soft gravitons. In this case the eikonal becomes an operator containing the creation and annihilation operators of the gravitons. The case of soft gravitons can be treated following the Bloch-Nordsieck approach and, in this case, I will be computing two other observables: the zero-frequency limit (ZFL) of the spectrum dE/d\omega of the emitted radiation and the angular momentum loss at 2PM and 3PM. I will consider also the case in which there are static modes localised at \(\omega=0\). In the third part of the seminar I will be discussing soft theorems with one graviton emission, first briefly at tree level, and then at loop level following the paper by Weinberg from 1965. Assuming the eikonal resummation and that all infrared divergences in the case of gravity come only from one loop diagrams, I will compute the universal soft terms, corresponding to \(\frac{1}{\omega}\), \(\log \omega\) and \(\omega \log^2 \omega\), first at the tree and one-loop level and then for the last two observables also at two-loop level. I will then use them to compute their contribution to the spectrum of emitted energy. Finally, if I have time left, I I will study the high energy limit. In particular, since the graviton is the massless particle with the highest spin, we expect universality at high energy. I will show that universality at high energy is satisfied both in the elastic and inelastic case, but this happens in the inelastic case in a very non trivial way. I will end with some conclusions and with a list of open problems.
Posted by: andrea
April 2024
Tue
30 Apr 2024
Novel observational signatures of early Universe physics
Willian Coulton
(Cambridge U)
Abstract:
Diverse observations have established the standard cosmological model, known as \(\Lambda CDM\). Within this model, the Universe began in a hot dense state filled with tiny primordial density fluctuations. These fluctuations grew as they collapsed under gravity and eventually became the seeds of the galaxies throughout the Universe. A key question is where did these initial perturbations come from? The leading model for their creation, known as inflation, posits that these arose from quantum vacuum fluctuations that were stretched to cosmic scales by a period of exponential expansion of the Universe. Many models predict that this process will leave distinct statistical signatures on the primordial density perturbations. In this talk I will discuss how we can use the spatial distribution of galaxies to search for these early Universe signatures. In particular, I will show how novel analysis methods will allow us to robustly disentangle the primordial information from late-time physics. These approaches will shed new light on aspects from the number of fields present during inflation to the strength of interactions to symmetries of inflation.
Diverse observations have established the standard cosmological model, known as \(\Lambda CDM\). Within this model, the Universe began in a hot dense state filled with tiny primordial density fluctuations. These fluctuations grew as they collapsed under gravity and eventually became the seeds of the galaxies throughout the Universe. A key question is where did these initial perturbations come from? The leading model for their creation, known as inflation, posits that these arose from quantum vacuum fluctuations that were stretched to cosmic scales by a period of exponential expansion of the Universe. Many models predict that this process will leave distinct statistical signatures on the primordial density perturbations. In this talk I will discuss how we can use the spatial distribution of galaxies to search for these early Universe signatures. In particular, I will show how novel analysis methods will allow us to robustly disentangle the primordial information from late-time physics. These approaches will shed new light on aspects from the number of fields present during inflation to the strength of interactions to symmetries of inflation.
Posted by: IC2
Tue
30 Apr 2024
Conformal geometry from entanglement
📍 London
Bowen Shi
(UCSD)
Abstract:
In a physical system with conformal symmetry, observables depend on cross-ratios, measures of distance invariant under global conformal transformations (conformal geometry for short). We identify a quantum information-theoretic mechanism by which the conformal geometry emerges at the gapless edge of a 2+1D quantum many-body system with a bulk energy gap. We introduce a novel pair of information-theoretic quantities (c,n) that can be defined locally on the edge from the wavefunction of the many-body system, without prior knowledge of any distance measure. We posit that, for a topological groundstate, the quantity c is stationary under arbitrary variations of the quantum state, and study the logical consequences. We show that stationarity, modulo an entanglement-based assumption about the bulk, implies (i) c is a non-negative constant that can be interpreted as the total central charge of the edge theory. (ii) n is a cross-ratio, obeying the full set of mathematical consistency rules, which further indicates the existence of a distance measure of the edge with global conformal invariance. Thus, the conformal geometry emerges from a simple assumption on groundstate entanglement. The stationarity of c is equivalent to a vector fixed-point equation involving n, making our assumption locally checkable. If time permits, we discuss a class of modular flow on a disk, which creates only edge excitations. We intuitively explain why Virasoro algebra can be revealed from a single wavefunction by analyzing such modular flows.
In a physical system with conformal symmetry, observables depend on cross-ratios, measures of distance invariant under global conformal transformations (conformal geometry for short). We identify a quantum information-theoretic mechanism by which the conformal geometry emerges at the gapless edge of a 2+1D quantum many-body system with a bulk energy gap. We introduce a novel pair of information-theoretic quantities (c,n) that can be defined locally on the edge from the wavefunction of the many-body system, without prior knowledge of any distance measure. We posit that, for a topological groundstate, the quantity c is stationary under arbitrary variations of the quantum state, and study the logical consequences. We show that stationarity, modulo an entanglement-based assumption about the bulk, implies (i) c is a non-negative constant that can be interpreted as the total central charge of the edge theory. (ii) n is a cross-ratio, obeying the full set of mathematical consistency rules, which further indicates the existence of a distance measure of the edge with global conformal invariance. Thus, the conformal geometry emerges from a simple assumption on groundstate entanglement. The stationarity of c is equivalent to a vector fixed-point equation involving n, making our assumption locally checkable. If time permits, we discuss a class of modular flow on a disk, which creates only edge excitations. We intuitively explain why Virasoro algebra can be revealed from a single wavefunction by analyzing such modular flows.
Posted by: QMW
Fri
26 Apr 2024
Non-invertible symmetries for qubits
📍 London
Shu-Heng Shao
(Stony Brook)
Abstract:
I'll discuss the exact non-invertible Kramers-Wannier symmetry of 1+1d lattice models on a tensor product Hilbert space of qubits. This symmetry mixes with lattice translations, and obeys a different algebra compared to the continuum one. The non-invertible symmetry leads to a constraint similar to that of Lieb-Schultz-Mattis, implying that the system cannot have a unique gapped ground state. It is either in a gapless phase or in a gapped phase with three (or a multiple of three) ground states, associated with the spontaneous breaking of the non-invertible symmetry.
I'll discuss the exact non-invertible Kramers-Wannier symmetry of 1+1d lattice models on a tensor product Hilbert space of qubits. This symmetry mixes with lattice translations, and obeys a different algebra compared to the continuum one. The non-invertible symmetry leads to a constraint similar to that of Lieb-Schultz-Mattis, implying that the system cannot have a unique gapped ground state. It is either in a gapless phase or in a gapped phase with three (or a multiple of three) ground states, associated with the spontaneous breaking of the non-invertible symmetry.
Posted by: QMW
Thu
25 Apr 2024
Lonti: Geodesics and Singularity Theorems in General Relativity (4/4)
Sunil Mukhi
(IISER, Pune)
Abstract:
These lectures will summarise mathematical aspects of classical General Relativity that are helpful in understanding current developments in the field. Lecture I will focus on Lorentzian-signature geometry, with an emphasis on causal structure. Some topological notions will also be introduced. In Lecture II we will go on to study the behaviour of geodesics in General Relativity and derive the famous Raychaudhuri equation. The null version of this equation, due to Sachs, will also be derived. Lecture III will focus on the "Hawking singularity theorem", namely that cosmological spacetimes with positive local Hubble constant are geodesically incomplete in the past under suitable conditions. In Lecture IV we will discuss the "Penrose singularity theorem" for black holes.
These lectures will summarise mathematical aspects of classical General Relativity that are helpful in understanding current developments in the field. Lecture I will focus on Lorentzian-signature geometry, with an emphasis on causal structure. Some topological notions will also be introduced. In Lecture II we will go on to study the behaviour of geodesics in General Relativity and derive the famous Raychaudhuri equation. The null version of this equation, due to Sachs, will also be derived. Lecture III will focus on the "Hawking singularity theorem", namely that cosmological spacetimes with positive local Hubble constant are geodesically incomplete in the past under suitable conditions. In Lecture IV we will discuss the "Penrose singularity theorem" for black holes.
Posted by: andrea
Thu
25 Apr 2024
From Correlators to massive amplitudes in N = 4 SYM
📍 London
Frank Coronado
(ETH Zurich)
Abstract:
In planar N=4 SYM, massless scattering amplitudes are dual to null
polygonal Wilson loops (T-duality) or the same as the
four-dimensional null limit of stress-tensor correlators. I will present
a (conjectured) generalization of this duality which equates correlators
of determinant operators, in a special ten-dimensional null limit, with
massive scattering amplitudes in the Coulomb branch of N=4. This
determinant operator is a generating function of all half-BPS
single-traces operators. By taming it on twistor space I will show its
correlators have ten dimensional poles which combine 4d space-time and
6d R-charge kinematics.
In planar N=4 SYM, massless scattering amplitudes are dual to null
polygonal Wilson loops (T-duality) or the same as the
four-dimensional null limit of stress-tensor correlators. I will present
a (conjectured) generalization of this duality which equates correlators
of determinant operators, in a special ten-dimensional null limit, with
massive scattering amplitudes in the Coulomb branch of N=4. This
determinant operator is a generating function of all half-BPS
single-traces operators. By taming it on twistor space I will show its
correlators have ten dimensional poles which combine 4d space-time and
6d R-charge kinematics.
Posted by: QMW
Wed
24 Apr 2024
Holography in the Gravitational Wave Era
📍 London
David Mateos
(ICC Universitat de Barcelona and ICREA)
Abstract:
The discovery of gravitational waves has opened a new experimental window into the Universe. The fact that the relevant dynamics is often out of equilibrium offers a golden opportunity for holography to make a unique impact on cosmology and astrophysics. I will illustrate this with applications to cosmological phase transitions, to neutron star mergers and to the BKL dynamics near a cosmological singularity.
The discovery of gravitational waves has opened a new experimental window into the Universe. The fact that the relevant dynamics is often out of equilibrium offers a golden opportunity for holography to make a unique impact on cosmology and astrophysics. I will illustrate this with applications to cosmological phase transitions, to neutron star mergers and to the BKL dynamics near a cosmological singularity.
Posted by: QMUL2
Wed
24 Apr 2024
On beta functions in the first-order sigma models
📍 London
Oleksandr Gamayun
(LIMS, London)
Abstract:
I will introduce a first-order formalism for two-dimensional sigma models with the Kähler target space. I will explain how to compute the metric beta function in this approach using the conformal perturbation methods. Comparing the answer with the standard geometric background field methods we observe certain anomalies, which we later resolve with supersymmetric completion. Based on 2312.01885 and 2307.04665.
I will introduce a first-order formalism for two-dimensional sigma models with the Kähler target space. I will explain how to compute the metric beta function in this approach using the conformal perturbation methods. Comparing the answer with the standard geometric background field methods we observe certain anomalies, which we later resolve with supersymmetric completion. Based on 2312.01885 and 2307.04665.
Posted by: andrea
Mon
22 Apr 2024
Lonti: Geodesics and Singularity Theorems in General Relativity (3/4)
Sunil Mukhi
(IISER, Pune)
Abstract:
These lectures will summarise mathematical aspects of classical General Relativity that are helpful in understanding current developments in the field. Lecture I will focus on Lorentzian-signature geometry, with an emphasis on causal structure. Some topological notions will also be introduced. In Lecture II we will go on to study the behaviour of geodesics in General Relativity and derive the famous Raychaudhuri equation. The null version of this equation, due to Sachs, will also be derived. Lecture III will focus on the "Hawking singularity theorem", namely that cosmological spacetimes with positive local Hubble constant are geodesically incomplete in the past under suitable conditions. In Lecture IV we will discuss the "Penrose singularity theorem" for black holes.
These lectures will summarise mathematical aspects of classical General Relativity that are helpful in understanding current developments in the field. Lecture I will focus on Lorentzian-signature geometry, with an emphasis on causal structure. Some topological notions will also be introduced. In Lecture II we will go on to study the behaviour of geodesics in General Relativity and derive the famous Raychaudhuri equation. The null version of this equation, due to Sachs, will also be derived. Lecture III will focus on the "Hawking singularity theorem", namely that cosmological spacetimes with positive local Hubble constant are geodesically incomplete in the past under suitable conditions. In Lecture IV we will discuss the "Penrose singularity theorem" for black holes.
Posted by: andrea
Fri
19 Apr 2024
Bootstrapping N = 4 sYM correlators using integrability
📍 London
Zahra Zahraee
(CERN)
Abstract:
In this talk we use integrability data to bootstrap correlation functions of planar maximally supersymmetric Yang- Mills theory. Focusing on four-point correlation function of stress-tensor, we first introduce a set of sum rules that are only sensitive to single-traces in the OPE expansion (this is advantageous because this data is available from integrability). We then discuss how these sum rules can be employed in numerical bootstrap to nonperturbatively bound planar OPE coefficients. We show rigorous bounds for the OPE coefficient of the Konishi operator at various t’Hooft couplings outside the perturbative regime. The talk is based on an ongoing work and 2207.01615.
In this talk we use integrability data to bootstrap correlation functions of planar maximally supersymmetric Yang- Mills theory. Focusing on four-point correlation function of stress-tensor, we first introduce a set of sum rules that are only sensitive to single-traces in the OPE expansion (this is advantageous because this data is available from integrability). We then discuss how these sum rules can be employed in numerical bootstrap to nonperturbatively bound planar OPE coefficients. We show rigorous bounds for the OPE coefficient of the Konishi operator at various t’Hooft couplings outside the perturbative regime. The talk is based on an ongoing work and 2207.01615.
Posted by: QMW
Thu
18 Apr 2024
Gravitational Wave Initiative
📍 London
Inaugural meeting
(Queen Mary University)
Abstract:
https://sites.google.com/view/gwiinauguralmeeting/home
https://sites.google.com/view/gwiinauguralmeeting/home
Posted by: QMW
Thu
18 Apr 2024
Lonti: Geodesics and Singularity Theorems in General Relativity (1/4)
Sunil Mukhi
(ICTS)
Abstract:
These lectures will summarise mathematical aspects of classical General Relativity that are helpful in understanding current developments in the field. Lecture I will focus on Lorentzian-signature geometry, with an emphasis on causal structure. Some topological notions will also be introduced. In Lecture II we will go on to study the behaviour of geodesics in General Relativity and derive the famous Raychaudhuri equation. The null version of this equation, due to Sachs, will also be derived. Lecture III will focus on the "Hawking singularity theorem", namely that cosmological spacetimes with positive local Hubble constant are geodesically incomplete in the past under suitable conditions. In Lecture IV we will discuss the "Penrose singularity theorem" for black holes.
These lectures will summarise mathematical aspects of classical General Relativity that are helpful in understanding current developments in the field. Lecture I will focus on Lorentzian-signature geometry, with an emphasis on causal structure. Some topological notions will also be introduced. In Lecture II we will go on to study the behaviour of geodesics in General Relativity and derive the famous Raychaudhuri equation. The null version of this equation, due to Sachs, will also be derived. Lecture III will focus on the "Hawking singularity theorem", namely that cosmological spacetimes with positive local Hubble constant are geodesically incomplete in the past under suitable conditions. In Lecture IV we will discuss the "Penrose singularity theorem" for black holes.
Posted by: andrea
Thu
18 Apr 2024
Lonti: Geodesics and Singularity Theorems in General Relativity (2/4)
Sunil Mukhi
(ICTS)
Abstract:
These lectures will summarise mathematical aspects of classical General Relativity that are helpful in understanding current developments in the field. Lecture I will focus on Lorentzian-signature geometry, with an emphasis on causal structure. Some topological notions will also be introduced. In Lecture II we will go on to study the behaviour of geodesics in General Relativity and derive the famous Raychaudhuri equation. The null version of this equation, due to Sachs, will also be derived. Lecture III will focus on the "Hawking singularity theorem", namely that cosmological spacetimes with positive local Hubble constant are geodesically incomplete in the past under suitable conditions. In Lecture IV we will discuss the "Penrose singularity theorem" for black holes.
These lectures will summarise mathematical aspects of classical General Relativity that are helpful in understanding current developments in the field. Lecture I will focus on Lorentzian-signature geometry, with an emphasis on causal structure. Some topological notions will also be introduced. In Lecture II we will go on to study the behaviour of geodesics in General Relativity and derive the famous Raychaudhuri equation. The null version of this equation, due to Sachs, will also be derived. Lecture III will focus on the "Hawking singularity theorem", namely that cosmological spacetimes with positive local Hubble constant are geodesically incomplete in the past under suitable conditions. In Lecture IV we will discuss the "Penrose singularity theorem" for black holes.
Posted by: andrea
Wed
17 Apr 2024
3d mirror symmetry with four supercharges
📍 London
Sergio Benvenuti
(INFN, Trieste)
Abstract:
3d mirror symmetry for theories with eight supercharges is understood in terms of Hanany-Witten brane setups and plays an important role in many areas of supersymmetric qft’s. The generalization to theories with four supercharges, in the non-Abelian case, has been a long standing open problem. In this talk, based on work with Riccardo Comi and Sara Pasquetti, we focus on brane setups with NS and D5’ branes, proposing that the related quiver gauge theories involve ‘improved bifundamentals’, that is strongly coupled SCFT's which are ancestors of the well known T[SU(N)] theories. Our proposal leads to 3d mirror dualities that can be exactly proven, reducing them to known Seiberg-like dualities. This gives strong support to the proposal. The simplest example is the duality between adjoint SQCD with F flavors, and a quiver with F-1 nodes and F-2 improved bifundamentals.
3d mirror symmetry for theories with eight supercharges is understood in terms of Hanany-Witten brane setups and plays an important role in many areas of supersymmetric qft’s. The generalization to theories with four supercharges, in the non-Abelian case, has been a long standing open problem. In this talk, based on work with Riccardo Comi and Sara Pasquetti, we focus on brane setups with NS and D5’ branes, proposing that the related quiver gauge theories involve ‘improved bifundamentals’, that is strongly coupled SCFT's which are ancestors of the well known T[SU(N)] theories. Our proposal leads to 3d mirror dualities that can be exactly proven, reducing them to known Seiberg-like dualities. This gives strong support to the proposal. The simplest example is the duality between adjoint SQCD with F flavors, and a quiver with F-1 nodes and F-2 improved bifundamentals.
Posted by: andrea
Thu
11 Apr 2024
Perturbed Black Holes: A CFT Approach and the Kerr-Binary-Problem
📍 London
Fabian Bautista
(IPhT)
Abstract:
In this talk we will discuss a new window into the solution of Heun differential equations arising in black hole perturbation theory using the tools of two-dimensional conformal field theory and gauge theories. Kerr Compton amplitudes for massless perturbation of generic spin-weight s, are written in compact form in terms of the so-called Nekrasov-Shatashvili functions; their symmetry properties are also discussed. These are then used as building blocks to study the scattering of two Kerr black holes with generic spin orientation. Comparison to conservative observables for bounded systems computed via first-order gravitational self-force methods are shown.
In this talk we will discuss a new window into the solution of Heun differential equations arising in black hole perturbation theory using the tools of two-dimensional conformal field theory and gauge theories. Kerr Compton amplitudes for massless perturbation of generic spin-weight s, are written in compact form in terms of the so-called Nekrasov-Shatashvili functions; their symmetry properties are also discussed. These are then used as building blocks to study the scattering of two Kerr black holes with generic spin orientation. Comparison to conservative observables for bounded systems computed via first-order gravitational self-force methods are shown.
Posted by: QMW
Wed
10 Apr 2024
Euclidean Wormholes in Holography and their relation to Wilson Loops
📍 London
Olga Papadoulaki
(Ecole Polytechnique)
Abstract:
Euclidean wormholes are exotic types of gravitational solutions that still challenge our physical intuition and understanding. After reviewing universal properties of asymptotically AdS wormhole solutions from a gravitational (bulk) point of view and the paradoxes they raise, I will describe some concrete (microscopic) field theoretic setups and models that exhibit such properties. These models can be reduced to matrix integrals and crucially involve correlated ("entangled") sums of representations of the boundary symmetry group. I will conclude with the realisation of such set-up in N=4 SYM/type IIB SUGRA.
Euclidean wormholes are exotic types of gravitational solutions that still challenge our physical intuition and understanding. After reviewing universal properties of asymptotically AdS wormhole solutions from a gravitational (bulk) point of view and the paradoxes they raise, I will describe some concrete (microscopic) field theoretic setups and models that exhibit such properties. These models can be reduced to matrix integrals and crucially involve correlated ("entangled") sums of representations of the boundary symmetry group. I will conclude with the realisation of such set-up in N=4 SYM/type IIB SUGRA.
Posted by: andrea
Thu
4 Apr 2024
The NLO Scattering Waveform and Linear-in-Spin Corrections
📍 London
Lara Bohnenblust
(University of Zurich)
Abstract:
Next-generation gravitational-wave detectors, operating in lower frequency ranges, will explore new types of systems including fly-bys, captures, eccentric configurations and high spin, that are well described within a weak-field approximation. I will discuss our recent NLO waveform computation for black-hole scattering in the Post-Minkowskian approximation, including linear-in-spin corrections, following Ref. [2312.14859]. The result is obtained from five point one-loop scattering amplitudes including massive scalars, vectors and a graviton, and computations are performed in the numerical unitarity framework. Special emphasis is put on the treatment of the "cut term" in the observable-based approach of Kosower, Maybee and O’Connell. The result includes IR and UV divergences and I will explain their origin and their treatment to obtain a finite observable.
Next-generation gravitational-wave detectors, operating in lower frequency ranges, will explore new types of systems including fly-bys, captures, eccentric configurations and high spin, that are well described within a weak-field approximation. I will discuss our recent NLO waveform computation for black-hole scattering in the Post-Minkowskian approximation, including linear-in-spin corrections, following Ref. [2312.14859]. The result is obtained from five point one-loop scattering amplitudes including massive scalars, vectors and a graviton, and computations are performed in the numerical unitarity framework. Special emphasis is put on the treatment of the "cut term" in the observable-based approach of Kosower, Maybee and O’Connell. The result includes IR and UV divergences and I will explain their origin and their treatment to obtain a finite observable.
Posted by: QMW
March 2024
Tue
26 Mar 2024
Entanglement, soft modes and celestial holography
📍 London
Ana-Maria Raclariu
(Amsterdam University)
Abstract:
In this talk I will start by revisiting the calculation of entanglement entropy in free Maxwell theory in 3+1 dimensional Minkowski spacetime. I will characterize the soft sector associated with a subregion and demonstrate that conformally soft mode configurations at the entangling surface, or equivalently correlated fluctuations in the large gauge charges of the subregion and its complement, give a non-trivial contribution to the entanglement entropy across a cut of future null infinity. I will conclude with some comments on the holographic description of bulk subregions in asymptotically flat spacetimes.
In this talk I will start by revisiting the calculation of entanglement entropy in free Maxwell theory in 3+1 dimensional Minkowski spacetime. I will characterize the soft sector associated with a subregion and demonstrate that conformally soft mode configurations at the entangling surface, or equivalently correlated fluctuations in the large gauge charges of the subregion and its complement, give a non-trivial contribution to the entanglement entropy across a cut of future null infinity. I will conclude with some comments on the holographic description of bulk subregions in asymptotically flat spacetimes.
Posted by: QMW
Thu
21 Mar 2024
Cosmological Correlators in Momentum Space
📍 London
Chandramouli Chowdhury
(University of Southampton)
Abstract:
Cosmological Correlators are one of the physical quantities that are of interest to cosmologists and are also of theoretical interest as they are related to CFT correlators via the AdS/CFT correspondence. These differ from the S-matrix as they are correlation functions computed on a given time slice. In this talk, I will review some progress in computing these in momentum space and also describe its relation to the S-matrix.
Cosmological Correlators are one of the physical quantities that are of interest to cosmologists and are also of theoretical interest as they are related to CFT correlators via the AdS/CFT correspondence. These differ from the S-matrix as they are correlation functions computed on a given time slice. In this talk, I will review some progress in computing these in momentum space and also describe its relation to the S-matrix.
Posted by: QMW
Wed
20 Mar 2024
SYK Model and de Sitter Space
Herman Verlinde
(Princeton)
Abstract:
an informal in-person seminar by Prof. Herman Verlinde
an informal in-person seminar by Prof. Herman Verlinde
Posted by: oxford
Wed
20 Mar 2024
Modular Constraints on N=4 Yang-Mills / Type IIB Superstring Holography
Daniele Dorigoni
(Durham)
Abstract:
I will describe a surprisingly simple representation of a class of integrated correlation functions of four superconformal primaries in the stress tensor multiplet of N=4 supersymmetric Yang-Mills theory with arbitrary simple gauge group, G. I then present exact formulae for these integrated correlators which are manifestly invariant under GNO electro-magnetic duality. For classical gauge groups, G=SU(N), SO(N), USp(2N), In the large-N limit these correlators are interpreted via holography in terms of the low-energy expansion of type IIB superstring amplitudes in AdS_5XS^5 or an orientifold thereof. In this way I recover the SL(2,Z)-invariant BPS interactions, arising in type IIB superstring amplitudes in the flat-space limit. From the asymptotic nature of the 1/N expansion I furthermore reconstruct non-perturbative contributions which holographically correspond to (p,q)-string world-sheet instantons.
I will describe a surprisingly simple representation of a class of integrated correlation functions of four superconformal primaries in the stress tensor multiplet of N=4 supersymmetric Yang-Mills theory with arbitrary simple gauge group, G. I then present exact formulae for these integrated correlators which are manifestly invariant under GNO electro-magnetic duality. For classical gauge groups, G=SU(N), SO(N), USp(2N), In the large-N limit these correlators are interpreted via holography in terms of the low-energy expansion of type IIB superstring amplitudes in AdS_5XS^5 or an orientifold thereof. In this way I recover the SL(2,Z)-invariant BPS interactions, arising in type IIB superstring amplitudes in the flat-space limit. From the asymptotic nature of the 1/N expansion I furthermore reconstruct non-perturbative contributions which holographically correspond to (p,q)-string world-sheet instantons.
Posted by: IC2
Wed
20 Mar 2024
Bootstrapping gauge theories
📍 London
Yifei He
(LPENS, Paris)
Abstract:
We propose the Gauge Theory Bootstrap, a method to compute the pion S-matrix that describes the strongly coupled low energy physics of QCD and other similar gauge theories. The method looks for the most general S-matrix that matches at low energy the tree level amplitudes of the non-linear sigma model and at high energy, QCD sum rules and form factors. We compute pion scattering phase shifts for all partial waves with angular momentum \(\ell<=3\) up to 2 GeV and calculate the low energy ChiPT coefficients. This is a theoretical/numerical calculation that uses as only data the pion mass \(m_\pi\), pion decay constant \(f_{\pi}\) and the QCD parameters \(N_c=3\), \(N_f=2\), \(m_q\) and \(\alpha_s\). All results are in reasonable agreement with experiment. In particular, we find the \(\rho(770)\), \(f_2(1270)\) and \(\rho(1450)\) resonances and some initial indication of particle production near the resonances. The interplay between the UV gauge theory and low energy pion physics is an example of a general situation where we know the microscopic theory as well as the effective theory of long wavelength fluctuations but we want to solve the strongly coupled dynamics at intermediate energies. The bootstrap builds a bridge between the low and high energy by determining the consistent S-matrix that matches both and provides, in this case, a new direction to understand the strongly coupled physics of gauge theories. Based on work with Martin Kruczenski.
We propose the Gauge Theory Bootstrap, a method to compute the pion S-matrix that describes the strongly coupled low energy physics of QCD and other similar gauge theories. The method looks for the most general S-matrix that matches at low energy the tree level amplitudes of the non-linear sigma model and at high energy, QCD sum rules and form factors. We compute pion scattering phase shifts for all partial waves with angular momentum \(\ell<=3\) up to 2 GeV and calculate the low energy ChiPT coefficients. This is a theoretical/numerical calculation that uses as only data the pion mass \(m_\pi\), pion decay constant \(f_{\pi}\) and the QCD parameters \(N_c=3\), \(N_f=2\), \(m_q\) and \(\alpha_s\). All results are in reasonable agreement with experiment. In particular, we find the \(\rho(770)\), \(f_2(1270)\) and \(\rho(1450)\) resonances and some initial indication of particle production near the resonances. The interplay between the UV gauge theory and low energy pion physics is an example of a general situation where we know the microscopic theory as well as the effective theory of long wavelength fluctuations but we want to solve the strongly coupled dynamics at intermediate energies. The bootstrap builds a bridge between the low and high energy by determining the consistent S-matrix that matches both and provides, in this case, a new direction to understand the strongly coupled physics of gauge theories. Based on work with Martin Kruczenski.
Posted by: andrea
Mon
18 Mar 2024
Lonti: Gravity as an Effective Field Theory (4/4)
Claudia de Rham
(Imperial College)
Abstract:
CANCELLED due to an unforeseen speaker emergency.
CANCELLED due to an unforeseen speaker emergency.
Posted by: CityU2
Wed
13 Mar 2024
The view of a point: Wigner-Inonu contractions and the flat space limit of AdS scattering
📍 London
David Berenstein
(UCSB)
Abstract:
I will describe how to consider the flat space limit of scaterig in AdS relative to a point (where sacttering occurs). The kinematics is related to the Wigner-Inonu contraction. In particular, I will discuss how to take the proper limits of wave functions in AdS (times extra dimensions) to understand a notion of in states and out states and how a scattering amplitude should be conceived. This will make use of the embedding formalism, where the description of these wave functions is simple. I will show how these wave functions are related to other constructions in AdS/CFT and suggest how the Mellin parameters of these other setups arise from integral representations of the wave functions in terms of Schwinger parameters.
I will describe how to consider the flat space limit of scaterig in AdS relative to a point (where sacttering occurs). The kinematics is related to the Wigner-Inonu contraction. In particular, I will discuss how to take the proper limits of wave functions in AdS (times extra dimensions) to understand a notion of in states and out states and how a scattering amplitude should be conceived. This will make use of the embedding formalism, where the description of these wave functions is simple. I will show how these wave functions are related to other constructions in AdS/CFT and suggest how the Mellin parameters of these other setups arise from integral representations of the wave functions in terms of Schwinger parameters.
Posted by: QMW
Wed
13 Mar 2024
Vertex algebras in SUSY QFT across dimensions
📍 London
Mykola Dedushenko
(Simons Center for Geometry and Physics)
Abstract:
I will describe a construction relating the Vertex Operator Algebra (VOA) of a 4d N=2 superconformal field theory (SCFT) to the boundary VOA in 3d N=4 QFT, and to the VOA in 2d QFT. Besides unifying several known constructions, this also draws connections to many other interesting problems, among which are the novel rank-zero 3d N=4 SCFTs emerging in the high-temperature limit of a 4d SCFT "on the second sheet".
I will describe a construction relating the Vertex Operator Algebra (VOA) of a 4d N=2 superconformal field theory (SCFT) to the boundary VOA in 3d N=4 QFT, and to the VOA in 2d QFT. Besides unifying several known constructions, this also draws connections to many other interesting problems, among which are the novel rank-zero 3d N=4 SCFTs emerging in the high-temperature limit of a 4d SCFT "on the second sheet".
Posted by: QMW
Tue
12 Mar 2024
Lonti: Gravity as an Effective Field Theory (3/4)
Claudia de Rham
(Imperial College)
Abstract:
CANCELLED due to an unforeseen speaker emergency.
CANCELLED due to an unforeseen speaker emergency.
Posted by: CityU2
Tue
12 Mar 2024
MTC(M3,G): 3d Topological Order Labeled by Seifert Manifolds
📍 London
Jingxiang Wu
(Oxford)
Abstract:
We propose a correspondence between topological order in 2+1d and
Seifert three-manifolds together with a choice of ADE gauge group G.
Topological order in 2+1d is known to be characterised in terms of
modular tensor categories (MTCs), and we thus propose a relation
between MTCs and Seifert three-manifolds. The correspondence defines
for every Seifert manifold and choice of G a fusion category, which we
conjecture to be modular whenever the Seifert manifold has trivial
first homology group with coefficients in the centre of G. The
construction determines the spins of anyons and their S-matrix, and
provides a constructive way to determine the R- and F-symbols from
simple building blocks. We explore the possibility that this
correspondence provides an alternative classification of MTCs, which
is put to the test by realising all MTCs (unitary or non-unitary) with
rank r<=5 in terms of Seifert manifolds and a choice of Lie group G.
We propose a correspondence between topological order in 2+1d and
Seifert three-manifolds together with a choice of ADE gauge group G.
Topological order in 2+1d is known to be characterised in terms of
modular tensor categories (MTCs), and we thus propose a relation
between MTCs and Seifert three-manifolds. The correspondence defines
for every Seifert manifold and choice of G a fusion category, which we
conjecture to be modular whenever the Seifert manifold has trivial
first homology group with coefficients in the centre of G. The
construction determines the spins of anyons and their S-matrix, and
provides a constructive way to determine the R- and F-symbols from
simple building blocks. We explore the possibility that this
correspondence provides an alternative classification of MTCs, which
is put to the test by realising all MTCs (unitary or non-unitary) with
rank r<=5 in terms of Seifert manifolds and a choice of Lie group G.
Posted by: QMW
Thu
7 Mar 2024
Geometric conservation in curved spacetime and entropy
📍 London
Sinya Aoki
(Kyoto University)
Abstract:
In this talk, I provide an improved definition of new conserved quantities derived from the energy-momentum tensor in curved spacetime by introducing an additional scalar function.
I find that the conserved current and the associated conserved charge become geometric under a certain initial condition of the scalar function,
and show that such a conserved geometric current generally exists in curved spacetime.
Furthermore, I demonstrate that the geometric conserved current agrees with the entropy current for the perfect fluid,
thus the conserved charge is the total entropy of the system.
In this talk, I provide an improved definition of new conserved quantities derived from the energy-momentum tensor in curved spacetime by introducing an additional scalar function.
I find that the conserved current and the associated conserved charge become geometric under a certain initial condition of the scalar function,
and show that such a conserved geometric current generally exists in curved spacetime.
Furthermore, I demonstrate that the geometric conserved current agrees with the entropy current for the perfect fluid,
thus the conserved charge is the total entropy of the system.
Posted by: QMW
Wed
6 Mar 2024
Exploring thermal CFTs
Elli Pomoni
(DESY)
Abstract:
QFT at finite temperature can be studied via compactifying the time direction. Placing CFTs on this non-trivial manifold, a subgroup of conformal symmetries is broken. Nonetheless, it is possible to derive broken Ward identities, which provide novel constraints on the theory. These constraints not only systematically reproduce all known results, including an implicit formulation of the generalized Cardy formula, but also relate the thermal energy spectrum with the conformal spectrum. Moreover, novel sum rules for one-point functions of operators are derived. They allow the computation of one-point functions for light operators in terms of zero temperature data, as well as their asymptotic behavior for heavy operators.
QFT at finite temperature can be studied via compactifying the time direction. Placing CFTs on this non-trivial manifold, a subgroup of conformal symmetries is broken. Nonetheless, it is possible to derive broken Ward identities, which provide novel constraints on the theory. These constraints not only systematically reproduce all known results, including an implicit formulation of the generalized Cardy formula, but also relate the thermal energy spectrum with the conformal spectrum. Moreover, novel sum rules for one-point functions of operators are derived. They allow the computation of one-point functions for light operators in terms of zero temperature data, as well as their asymptotic behavior for heavy operators.
Posted by: IC2
Wed
6 Mar 2024
Staggered bosons
📍 London
David Berenstein
(UCSB)
Abstract:
I will discuss a novel construction of field theories based on the idea that one has only a half boson degree of freedom per lattice site. Basically, instead of having a pair of canonical conjugate commuting variables at each site, one has only one degree of freedom and the non-trivial commutators arise from connections to the nearest neighbors. The construction is very similar to staggered fermions and naturally produces gapless systems with interesting topological properties. When considering gauging discrete translations on the phase space in one dimensional examples, one gets interesting critical spin chains, examples of which include the critical Ising model in a transverse magnetic field and the 3-state Potts model at criticality. I will explain how these staggered boson variables are very natural for describing non-invertible symmetries.
These non-invertible symmetries are useful to describe the critical properties of these non-trivial spin chains.
Models in higher dimensions obtained this way can automatically produce dynamical systems of gapless fractons.
I will discuss a novel construction of field theories based on the idea that one has only a half boson degree of freedom per lattice site. Basically, instead of having a pair of canonical conjugate commuting variables at each site, one has only one degree of freedom and the non-trivial commutators arise from connections to the nearest neighbors. The construction is very similar to staggered fermions and naturally produces gapless systems with interesting topological properties. When considering gauging discrete translations on the phase space in one dimensional examples, one gets interesting critical spin chains, examples of which include the critical Ising model in a transverse magnetic field and the 3-state Potts model at criticality. I will explain how these staggered boson variables are very natural for describing non-invertible symmetries.
These non-invertible symmetries are useful to describe the critical properties of these non-trivial spin chains.
Models in higher dimensions obtained this way can automatically produce dynamical systems of gapless fractons.
Posted by: andrea
Tue
5 Mar 2024
Lonti: Gravity as an Effective Field Theory (2/4)
Claudia de Rham
(Imperial College)
Abstract:
CANCELLED due to an unforeseen speaker emergency.
CANCELLED due to an unforeseen speaker emergency.
Posted by: CityU2
Tue
5 Mar 2024
The String Landscape and the Swampland
Miguel Montero
(IFT/UAM)
Abstract:
It is natural to expect that quantum gravity is not directly relevant at the low energies which experimentally accesible today, since the Planck scale is many orders of magnitude above the electroweak scale. However, mounting evidence coming from String Theory compactifications, general considerations based on black hole evaporation and holography suggest that there are some constraints that must be satisfied by low-energy effective field theories coupled to Einsteinian gravity. These constraints can in principle be used to rule out models at low energies or to connect with observations, an effort dubbed the "Swampland Program". I will review the program, its motivation, and recent advances.
It is natural to expect that quantum gravity is not directly relevant at the low energies which experimentally accesible today, since the Planck scale is many orders of magnitude above the electroweak scale. However, mounting evidence coming from String Theory compactifications, general considerations based on black hole evaporation and holography suggest that there are some constraints that must be satisfied by low-energy effective field theories coupled to Einsteinian gravity. These constraints can in principle be used to rule out models at low energies or to connect with observations, an effort dubbed the "Swampland Program". I will review the program, its motivation, and recent advances.
Posted by: IC2
Mon
4 Mar 2024
Lonti: Gravity as an Effective Field Theory (1/4)
Claudia de Rham
(Imperial College)
Abstract:
CANCELLED due to an unforeseen speaker emergency.
CANCELLED due to an unforeseen speaker emergency.
Posted by: CityU2
February 2024
Thu
29 Feb 2024
Bounding Effective Field Theories: From flat space to FRW
📍 London
Mariana Carrillo Gonzales
(Imperial College)
Abstract:
Effective Field Theories (EFTs) allow us to describe low energy physics without knowing the specific UV completion. This comes at the cost of having free parameters (Wilson coefficients) whose values encode the UV physics, but are not constraint from a standard EFT point of view. It is well known that some values can lead to unphysical properties of these theories. In this talk, I will present a low energy technique to put bounds on these coefficients by requiring causal propagation. I will show how these bounds can be obtained in flat space and then move on to how apply these techniques in cosmological spacetimes. Throughout the talk I will present bounds on scalar and photon EFTs.
Effective Field Theories (EFTs) allow us to describe low energy physics without knowing the specific UV completion. This comes at the cost of having free parameters (Wilson coefficients) whose values encode the UV physics, but are not constraint from a standard EFT point of view. It is well known that some values can lead to unphysical properties of these theories. In this talk, I will present a low energy technique to put bounds on these coefficients by requiring causal propagation. I will show how these bounds can be obtained in flat space and then move on to how apply these techniques in cosmological spacetimes. Throughout the talk I will present bounds on scalar and photon EFTs.
Posted by: QMW
Wed
28 Feb 2024
Anomalies and Gauging of U(1) Symmetries
Francesco Benini
(SISSA)
Abstract:
The Symmetry TFT of a quantum field theory is a Topological Field
Theory in one dimension more, that describes the structure of the
symmetry, its representations, its anomalies, and the possible
topological manipulations (gaugings). Until recently only the case of
finite symmetries had been addressed. I will present a proposal for
the Symmetry TFT of theories with a U(1) symmetry: it is a BF theory
with a continuum of topological operators. I will discuss many
examples, including chiral anomalies, 2-groups, the non-invertible Q/Z
chiral symmetry in 4d with ABJ anomaly, and I will discuss the
non-Abelian case as well.
The Symmetry TFT of a quantum field theory is a Topological Field
Theory in one dimension more, that describes the structure of the
symmetry, its representations, its anomalies, and the possible
topological manipulations (gaugings). Until recently only the case of
finite symmetries had been addressed. I will present a proposal for
the Symmetry TFT of theories with a U(1) symmetry: it is a BF theory
with a continuum of topological operators. I will discuss many
examples, including chiral anomalies, 2-groups, the non-invertible Q/Z
chiral symmetry in 4d with ABJ anomaly, and I will discuss the
non-Abelian case as well.
Posted by: IC2
Wed
28 Feb 2024
A is for the ANEC
📍 London
Gregoire Mathys
(EPFL, Lausanne)
Abstract:
In this talk, I will discuss a connection between the ANEC (Averaged Null Energy Condition) operator and monotonicity of the renormalization group. In particular, I will show how the 2d c-theorem and 4d a-theorem can be derived using the ANEC. This derivation relies on contact terms appearing in specific ANEC correlators. I will also review a new infinite set of constraints that can be derived from the ANEC in 2d QFT. This program hints at a more general role for light-ray operators in QFT, which I will argue for.
In this talk, I will discuss a connection between the ANEC (Averaged Null Energy Condition) operator and monotonicity of the renormalization group. In particular, I will show how the 2d c-theorem and 4d a-theorem can be derived using the ANEC. This derivation relies on contact terms appearing in specific ANEC correlators. I will also review a new infinite set of constraints that can be derived from the ANEC in 2d QFT. This program hints at a more general role for light-ray operators in QFT, which I will argue for.
Posted by: andrea
Tue
27 Feb 2024
Infinite Permutation Groups and the Origin of Quantum Mechanics
Pavlos Kazakopoulos
(U Athens)
Abstract:
In this talk, we examine a fundamental question posed some time ago by Birkhoff and von Neumann: What are the possible structures of measurement in a theory of Physics? We find striking connections with the conceptual framework of First Order Logic, and apply classification theorems for the automorphism groups of first order relational structures to argue for the uniqueness of Hilbert space as the phase space of a theory with probabilistic transitions between atomic states. We discuss possible applications of these observations to Algebraic Quantum Field Theory.
In this talk, we examine a fundamental question posed some time ago by Birkhoff and von Neumann: What are the possible structures of measurement in a theory of Physics? We find striking connections with the conceptual framework of First Order Logic, and apply classification theorems for the automorphism groups of first order relational structures to argue for the uniqueness of Hilbert space as the phase space of a theory with probabilistic transitions between atomic states. We discuss possible applications of these observations to Algebraic Quantum Field Theory.
Posted by: IC2
Mon
26 Feb 2024
3d gravity from an ensemble of approximate CFTs
Gabriel Wong
(Oxford)
Abstract:
This is part of HoloUK2. Registration is free but space is limited, so please register at https://sites.google.com/view/holouk/home/holouk-2.
One of the major insights gained from holographic duality is the relation between the physics of black holes and quantum chaotic systems. This relation is made precise in the duality between two dimensional JT gravity and random matrix theory. In this work, we generalize this to a duality between AdS3 gravity and a random ensemble of approximate CFT's. The latter is described by a combined tensor and matrix model, describing the OPE coefficients and spectrum of a theory that approximately satisfies the bootstrap constraints. We show that the Feynman diagrams of the random ensemble produce a sum over 3 manifolds that agrees with the partition function of 3d gravity. A crucial element of this dictionary is the Virasoro TQFT, which defines the bulk gravitational path integral via the cutting and sewing relations of topological field theory. This TQFT has gravitational edge modes degrees of freedom whose entanglement gives rise to gravitational entropy.
This is part of HoloUK2. Registration is free but space is limited, so please register at https://sites.google.com/view/holouk/home/holouk-2.
One of the major insights gained from holographic duality is the relation between the physics of black holes and quantum chaotic systems. This relation is made precise in the duality between two dimensional JT gravity and random matrix theory. In this work, we generalize this to a duality between AdS3 gravity and a random ensemble of approximate CFT's. The latter is described by a combined tensor and matrix model, describing the OPE coefficients and spectrum of a theory that approximately satisfies the bootstrap constraints. We show that the Feynman diagrams of the random ensemble produce a sum over 3 manifolds that agrees with the partition function of 3d gravity. A crucial element of this dictionary is the Virasoro TQFT, which defines the bulk gravitational path integral via the cutting and sewing relations of topological field theory. This TQFT has gravitational edge modes degrees of freedom whose entanglement gives rise to gravitational entropy.
Posted by: andrea
Mon
26 Feb 2024
Black hole bulk-cone singularities
Matthew Dodelson
(CERN)
Abstract:
This is part of HoloUK2. Registration is free but space is limited, so please register at https://sites.google.com/view/holouk/home/holouk-2.
Correlators in field theories at finite temperatures have singularities on the light cone. Are there any other singularities? In this talk, I will address this question in the context of holographic theories in the black hole phase. Two points on the AdS boundary can be connected by a null geodesic in the bulk, leading to a so-called bulk-cone singularity. These new singularities were previously conjectured by analyzing the geodesic approximation, but we will derive them in full generality by developing the technology of thermal Regge theory. The functional form of the singularity leads to sharp signatures of the AdS photon sphere in the boundary CFT, including an identification of the boundary dual of the angular velocity and Lyapunov exponent associated with the photon sphere. I will also comment on the resolution of the singularity by stringy effects.
This is part of HoloUK2. Registration is free but space is limited, so please register at https://sites.google.com/view/holouk/home/holouk-2.
Correlators in field theories at finite temperatures have singularities on the light cone. Are there any other singularities? In this talk, I will address this question in the context of holographic theories in the black hole phase. Two points on the AdS boundary can be connected by a null geodesic in the bulk, leading to a so-called bulk-cone singularity. These new singularities were previously conjectured by analyzing the geodesic approximation, but we will derive them in full generality by developing the technology of thermal Regge theory. The functional form of the singularity leads to sharp signatures of the AdS photon sphere in the boundary CFT, including an identification of the boundary dual of the angular velocity and Lyapunov exponent associated with the photon sphere. I will also comment on the resolution of the singularity by stringy effects.
Posted by: andrea
Thu
22 Feb 2024
Twisting integrability
📍 London
Sibylle Driezen
(ETH Zurich)
Abstract:
Recent years have seen an upsurge of interest in deformations of
two-dimensional sigma-models which preserve classical integrability.
Integrability is known to offer powerful techniques for solving such
models exactly, even in complex scenarios such as at strong coupling.
This talk introduces classical integrability, and the role played by
worldsheet dualities in the development of a large family of integrable
deformations. The second part of the talk focuses on the application of
these deformations within the AdS/CFT correspondence, in order to obtain
exact methods for addressing gauge and gravity theories with reduced
Noether (super)symmetries. However, current "AdS/CFT integrability"
methods are mostly restricted to the undeformed, maximally
(super)symmetric instances. To enhance their applicability to a broader
range of theoretical models, the concept of “twisted†AdS/CFT
integrability is introduced, specifically targeting the “Jordanianâ€
subclass of integrable deformations. Recent and ongoing work in this
area will be discussed.
Recent years have seen an upsurge of interest in deformations of
two-dimensional sigma-models which preserve classical integrability.
Integrability is known to offer powerful techniques for solving such
models exactly, even in complex scenarios such as at strong coupling.
This talk introduces classical integrability, and the role played by
worldsheet dualities in the development of a large family of integrable
deformations. The second part of the talk focuses on the application of
these deformations within the AdS/CFT correspondence, in order to obtain
exact methods for addressing gauge and gravity theories with reduced
Noether (super)symmetries. However, current "AdS/CFT integrability"
methods are mostly restricted to the undeformed, maximally
(super)symmetric instances. To enhance their applicability to a broader
range of theoretical models, the concept of “twisted†AdS/CFT
integrability is introduced, specifically targeting the “Jordanianâ€
subclass of integrable deformations. Recent and ongoing work in this
area will be discussed.
Posted by: QMW
Wed
21 Feb 2024
Dimensionally Reducing Generalized Symmetries from (3+1)-Dimensions
Gabi Zafrir
(University of Haifa)
Abstract:
Recently there has been a renewed interest in the subject of novel types of symmetries, now known as generalized symmetries. An interesting question is what happens to these more general symmetry structures upon compactification to lower dimensions. In this talk, we shall explore this in the context of the compactification of 4d N=1 SCFTs to 2d on spheres.
Recently there has been a renewed interest in the subject of novel types of symmetries, now known as generalized symmetries. An interesting question is what happens to these more general symmetry structures upon compactification to lower dimensions. In this talk, we shall explore this in the context of the compactification of 4d N=1 SCFTs to 2d on spheres.
Posted by: IC2
Wed
21 Feb 2024
The Come-back of Carroll
📍 London
Eric Bergshoeff
(University of Groningen)
Abstract:
Carroll symmetries were introduced many years ago by Levy-Leblond and Gupta as a possible contraction of the Lorentz symmetries in which effectively the speed of light is sent to zero. The name was inspired by the bizarre property that Carroll particles cannot move. After many years of silence Carroll symmetries have returned to the stage since they have been recognized as symmetries that do occur in several special situations such as the horizon of a black hole. In this presentation I will discuss some of the basic properties and mysteries of Carroll symmetries.
Carroll symmetries were introduced many years ago by Levy-Leblond and Gupta as a possible contraction of the Lorentz symmetries in which effectively the speed of light is sent to zero. The name was inspired by the bizarre property that Carroll particles cannot move. After many years of silence Carroll symmetries have returned to the stage since they have been recognized as symmetries that do occur in several special situations such as the horizon of a black hole. In this presentation I will discuss some of the basic properties and mysteries of Carroll symmetries.
Posted by: andrea
Mon
19 Feb 2024
Lonti: CFTs in Lorentzian signature (4/4)
Petr Kravchuk
(King's)
Abstract:
In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.
In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.
Posted by: andrea
Thu
15 Feb 2024
Kerr binary dynamics from minimal coupling and double copy
📍 London
Francesco Alessio
(Nordita)
Abstract:
I will show how to construct a Lagrangian based on a notion of minimal coupling that includes classical spin effects that is relevant to describe Kerr binaries in the post-Minkowski (PM) regime. Using such Lagrangian, I will derive expressions for the classical amplitude for the elastic 2—>2 process at 1PM and 2PM. I will then consider radiation reaction effects and their connection to the imaginary part of the 3PM spinning eikonal phase.
I will show how to construct a Lagrangian based on a notion of minimal coupling that includes classical spin effects that is relevant to describe Kerr binaries in the post-Minkowski (PM) regime. Using such Lagrangian, I will derive expressions for the classical amplitude for the elastic 2—>2 process at 1PM and 2PM. I will then consider radiation reaction effects and their connection to the imaginary part of the 3PM spinning eikonal phase.
Posted by: QMW
Wed
14 Feb 2024
The AdS Virasoro-Shapiro amplitude
Tobias Hansen
(Durham University)
Abstract:
I will present a constructive method to compute the Virasoro-Shapiro amplitude on AdS5xS5, order by order in AdS curvature corrections. The k-th curvature correction takes the form of a genus zero world-sheet integral involving single-valued multiple polylogarithms of weight 3k. The coefficients in an ansatz in terms of these functions are fixed by Regge boundedness of the amplitude, which is imposed via a dispersion relation in the holographically dual CFT. We explicitly constructed the first two curvature corrections. Our final answer reproduces all CFT data available from integrability and all localisation results, to this order, and produces a wealth of new CFT data for planar N=4 SYM theory at strong coupling. Finally, the high energy limit of the AdS Virasoro-Shapiro amplitude is compared to a classical scattering computation in AdS and agreement is found.
I will present a constructive method to compute the Virasoro-Shapiro amplitude on AdS5xS5, order by order in AdS curvature corrections. The k-th curvature correction takes the form of a genus zero world-sheet integral involving single-valued multiple polylogarithms of weight 3k. The coefficients in an ansatz in terms of these functions are fixed by Regge boundedness of the amplitude, which is imposed via a dispersion relation in the holographically dual CFT. We explicitly constructed the first two curvature corrections. Our final answer reproduces all CFT data available from integrability and all localisation results, to this order, and produces a wealth of new CFT data for planar N=4 SYM theory at strong coupling. Finally, the high energy limit of the AdS Virasoro-Shapiro amplitude is compared to a classical scattering computation in AdS and agreement is found.
Posted by: IC2
Wed
14 Feb 2024
Vacua in locally de Sitter cosmologies, and how to distinguish them
📍 London
Jorma Louko
(Nottingham U.)
Abstract:
de Sitter spacetime admits distinct Friedmann-Robertson-Walker foliations with cosh, sinh and exponential time evolution laws. In three or more spacetime dimensions, these foliations have respectively positive, negative and vanishing spatial curvature. In two spacetime dimensions, by contrast, there is no spatial curvature, and all three evolution laws allow spatial sections with S^1 topology and a freely specifiable spatial circumference parameter. We identify geometrically preferred quantum states for a massive scalar field on these locally de Sitter 1+1 cosmologies, some singled out by adiabatic criteria, others induced from the Euclidean vacuum by a quotient construction. We show how a comoving quantum observer, modelled as an Unruh-DeWitt detector, can distinguish these states by local measurements. (Joint work with Vladimir Toussaint, 2304.10395)
de Sitter spacetime admits distinct Friedmann-Robertson-Walker foliations with cosh, sinh and exponential time evolution laws. In three or more spacetime dimensions, these foliations have respectively positive, negative and vanishing spatial curvature. In two spacetime dimensions, by contrast, there is no spatial curvature, and all three evolution laws allow spatial sections with S^1 topology and a freely specifiable spatial circumference parameter. We identify geometrically preferred quantum states for a massive scalar field on these locally de Sitter 1+1 cosmologies, some singled out by adiabatic criteria, others induced from the Euclidean vacuum by a quotient construction. We show how a comoving quantum observer, modelled as an Unruh-DeWitt detector, can distinguish these states by local measurements. (Joint work with Vladimir Toussaint, 2304.10395)
Posted by: andrea
Wed
14 Feb 2024
Thermodynamics of near-extreme Kerr
📍 London
Chiara Toldo
(Harvard)
Abstract:
From the perspective of classical gravity, a black hole is the simplest object we know of. At the same time, it possesses huge entropy, hinting at an incredibly complex microstructure: understanding this fact falls in the realm of quantum gravity. In this talk I will review recent results concerning the microscopics and the thermodynamics of the fast spinning black holes, and I will describe how recently developed techniques allow to compute the quantum corrections to the entropy of near-extremal Kerr black holes. The quantum-corrected near-extremal entropy exhibits 3/2logT behavior characteristic of the Schwarzian model and predicts a lifting of the ground state degeneracy for the extremal Kerr black hole.
From the perspective of classical gravity, a black hole is the simplest object we know of. At the same time, it possesses huge entropy, hinting at an incredibly complex microstructure: understanding this fact falls in the realm of quantum gravity. In this talk I will review recent results concerning the microscopics and the thermodynamics of the fast spinning black holes, and I will describe how recently developed techniques allow to compute the quantum corrections to the entropy of near-extremal Kerr black holes. The quantum-corrected near-extremal entropy exhibits 3/2logT behavior characteristic of the Schwarzian model and predicts a lifting of the ground state degeneracy for the extremal Kerr black hole.
Posted by: QMW
Tue
13 Feb 2024
Crystalline topological matter in and out of equilibrium
Frank Schindler
(Imperial College London)
Abstract:
I’ll give a pedagogical introduction to some conceptual aspects of quantum materials in and out of equilibrium. Such materials, capable of realising exotic states of matter, hold promise for manifold applications in areas like microelectronics and quantum computing. The most basic quantum materials are electronic band insulators. My talk will start with an explanation of how they can be categorised based on crystalline symmetry and topology. Following this, I will broaden the framework of band topology to include non-Hermitian Hamiltonians, which describe systems that are not in equilibrium. To conclude my talk, I will delve into a curious connection between Hermitian bulk and non-Hermitian boundary topological invariants.
I’ll give a pedagogical introduction to some conceptual aspects of quantum materials in and out of equilibrium. Such materials, capable of realising exotic states of matter, hold promise for manifold applications in areas like microelectronics and quantum computing. The most basic quantum materials are electronic band insulators. My talk will start with an explanation of how they can be categorised based on crystalline symmetry and topology. Following this, I will broaden the framework of band topology to include non-Hermitian Hamiltonians, which describe systems that are not in equilibrium. To conclude my talk, I will delve into a curious connection between Hermitian bulk and non-Hermitian boundary topological invariants.
Posted by: IC2
Mon
12 Feb 2024
Lonti: CFTs in Lorentzian signature (3/4)
Petr Kravchuk
(King's)
Abstract:
In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.
In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.
Posted by: andrea
Mon
12 Feb 2024
Topology change and non-geometry at infinite distance
📍 London
Saskia Demulder
(Ben Gurion U.)
Abstract:
The Swampland program aims at formulating a complete set of criteria in order to identify theories that can be uplifted in the UV to a theory of quantum gravity. The distance conjecture in particular diagnoses viable low energy effective theories by examining their breakdown at infinite distance in their parameter space. At the same time, infinite distance points in parameter space are naturally intertwined with string dualities and in particular T-duality. In this talk, we will show that this relation becomes much richer and intricate when the internal space is curved or supported by fluxes. Consistency of T-duality then leads us to suggest an extension to the Swampland distance conjecture. This work is in collaboration with Thomas Raml and Dieter Lüst.
The Swampland program aims at formulating a complete set of criteria in order to identify theories that can be uplifted in the UV to a theory of quantum gravity. The distance conjecture in particular diagnoses viable low energy effective theories by examining their breakdown at infinite distance in their parameter space. At the same time, infinite distance points in parameter space are naturally intertwined with string dualities and in particular T-duality. In this talk, we will show that this relation becomes much richer and intricate when the internal space is curved or supported by fluxes. Consistency of T-duality then leads us to suggest an extension to the Swampland distance conjecture. This work is in collaboration with Thomas Raml and Dieter Lüst.
Posted by: andrea
Mon
12 Feb 2024
Simon Norton Memorial Lecture
Leonard Soicher
(QML)
Abstract:
The London Institute is honoured to have been asked by Simon Norton's family to organise an annual lecture in memory of Simon. Last year we had a wonderful inaugural lecture by Prof. Peter Cameron.
In the second Simon Norton Lecture, Prof. Leonard Soicher will explain what the monster is and its importance.
Please register (free) at
https://lims.ac.uk/event/a-friendly-monster/
The London Institute is honoured to have been asked by Simon Norton's family to organise an annual lecture in memory of Simon. Last year we had a wonderful inaugural lecture by Prof. Peter Cameron.
In the second Simon Norton Lecture, Prof. Leonard Soicher will explain what the monster is and its importance.
Please register (free) at
https://lims.ac.uk/event/a-friendly-monster/
Posted by: oxford
Mon
12 Feb 2024
Inaugural Simon Norton Lecture: A Monstrous Talent
Peter Cameron
(St Andrews and Queen Mary)
Abstract:
In the inaugural Simon Norton Lecture, Prof. Peter Cameron will celebrate the mathematician's achievements and talk about Norton algebras.
https://lims.ac.uk/event/a-monstrous-talent/
In the inaugural Simon Norton Lecture, Prof. Peter Cameron will celebrate the mathematician's achievements and talk about Norton algebras.
https://lims.ac.uk/event/a-monstrous-talent/
Posted by: oxford
Wed
7 Feb 2024
Double-scaled SYK and de Sitter Holography
📍 London
Vladimir Narovlansky
(Princeton U.)
Abstract:
Double-scaled SYK (DSSYK) is a model with interesting dynamics, and many known exact results. Yet, the gravitational behavior of the system is not fully understood. I will discuss the reasoning behind a suggested connection between DSSYK and de Sitter holography. We will mention the general form of the correspondence as well as the mapping of parameters between the two sides. On the SYK side we consider two copies of DSSYK at infinite temperature with an equal energy constraint. We will discuss explicitly the two-point function in double-scaled SYK and compare it to de Sitter.
Double-scaled SYK (DSSYK) is a model with interesting dynamics, and many known exact results. Yet, the gravitational behavior of the system is not fully understood. I will discuss the reasoning behind a suggested connection between DSSYK and de Sitter holography. We will mention the general form of the correspondence as well as the mapping of parameters between the two sides. On the SYK side we consider two copies of DSSYK at infinite temperature with an equal energy constraint. We will discuss explicitly the two-point function in double-scaled SYK and compare it to de Sitter.
Posted by: andrea
Wed
7 Feb 2024
Emergence of space and time in holography
📍 London
Hong Liu
(MIT)
Abstract:
In holographic duality, a higher dimensional quantum gravity system is equivalent to a lower dimensional conformal field theory (CFT) with a large number of degrees of freedom. In this talk, I will introduce a framework to describe using the CFT how geometric notions in the gravity system, such as spacetime subregions, different notions of times, causal structure, and spacetime connectivity, emerge in the semi-classical limit.
In holographic duality, a higher dimensional quantum gravity system is equivalent to a lower dimensional conformal field theory (CFT) with a large number of degrees of freedom. In this talk, I will introduce a framework to describe using the CFT how geometric notions in the gravity system, such as spacetime subregions, different notions of times, causal structure, and spacetime connectivity, emerge in the semi-classical limit.
Posted by: andrea
Tue
6 Feb 2024
Higher-twist Regge trajectories in CFTs
Petr Kravchuk
(King's College London)
Abstract:
Abstract: On general grounds, the spectrum of a Conformal Field Theory (CFT) is expected to be extremely complicated away from special limits. One of such limits consists of the lowest energy states for every given spin, which are also known as the leading-twist states. In this talk I will discuss the structures that emerge in the spectrum as one departs from this limit towards the higher-twist states, focusing especially on the Regge trajectories. In particular, I will describe a general mechanism that reconciles the idea of Regge trajectories with the growing number of local operators at large spin. I will then demonstrate how this mechanism works in the case of one-loop phi^4 Wilson-Fisher theory in epsilon-expansion. This example will also clarify the properties of double-twist trajectories and light-cone bootstrap at higher-twist. Finally, I will briefly discuss a work in progress on going beyond the double-twist limit.
Abstract: On general grounds, the spectrum of a Conformal Field Theory (CFT) is expected to be extremely complicated away from special limits. One of such limits consists of the lowest energy states for every given spin, which are also known as the leading-twist states. In this talk I will discuss the structures that emerge in the spectrum as one departs from this limit towards the higher-twist states, focusing especially on the Regge trajectories. In particular, I will describe a general mechanism that reconciles the idea of Regge trajectories with the growing number of local operators at large spin. I will then demonstrate how this mechanism works in the case of one-loop phi^4 Wilson-Fisher theory in epsilon-expansion. This example will also clarify the properties of double-twist trajectories and light-cone bootstrap at higher-twist. Finally, I will briefly discuss a work in progress on going beyond the double-twist limit.
Posted by: IC2
Mon
5 Feb 2024
Lonti: CFTs in Lorentzian signature (2/4)
Petr Kravchuk
(King's)
Abstract:
In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.
In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.
Posted by: andrea
Thu
1 Feb 2024
From Gravity's Attractive Blocks to Matrix Models and Back
📍 London
Morteza Hosseini
(Imperial College)
Abstract:
The quest to understand the microscopic origins of Bekenstein-Hawking entropy has been a longstanding challenge for physicists. In the context of AdS black holes, this entropy is expected to be explicable in terms of the states of the holographic dual quantum field theory, as per the AdS/CFT framework. In my talk, I will introduce the idea of gluing gravitational blocks for supersymmetric AdS black holes in String/M-theory with arbitrary rotation and generic electric and magnetic charges. This approach provides insights into the large N behavior of the partition function of the corresponding holographic dual field theory. Time permitting, I will also delve into the partition function of the 6d (2, 0) theory on S^2 x M_3, where M_3 is either a three-sphere or S^2 x S^1, and analyse its large N behaviour.
The quest to understand the microscopic origins of Bekenstein-Hawking entropy has been a longstanding challenge for physicists. In the context of AdS black holes, this entropy is expected to be explicable in terms of the states of the holographic dual quantum field theory, as per the AdS/CFT framework. In my talk, I will introduce the idea of gluing gravitational blocks for supersymmetric AdS black holes in String/M-theory with arbitrary rotation and generic electric and magnetic charges. This approach provides insights into the large N behavior of the partition function of the corresponding holographic dual field theory. Time permitting, I will also delve into the partition function of the 6d (2, 0) theory on S^2 x M_3, where M_3 is either a three-sphere or S^2 x S^1, and analyse its large N behaviour.
Posted by: QMW
January 2024
Wed
31 Jan 2024
On the class S origin of discs and spindles
Pieter Bomans
(Oxford)
Abstract:
In this talk, we delve into the world of spindle and disc solutions dual to 4d SCFTs. Despite extensive studies conducted over the years, certain aspects continue to challenge our understanding. Disc solutions, conjectured to be dual to Argyres-Douglas theories, present a puzzle as at first sight the symmetries do not match across the holographic correspondence. The spindle solutions, on the other hand, completely lack a proper understanding of their dual field theories.
This talk aims to shed light on these puzzles, offering a detailed explanation for the breaking of the unwanted symmetry in disc solution. Furthermore, we will clarify various aspects of the spindle solution, contributing to a more profound understanding of the class S origin of the dual SCFTs.
As a byproduct, we enlarge the class of holographic surface defects of the (2,0) theory as well as provide a concrete description of a class of locally N=1 preserving punctures.
In this talk, we delve into the world of spindle and disc solutions dual to 4d SCFTs. Despite extensive studies conducted over the years, certain aspects continue to challenge our understanding. Disc solutions, conjectured to be dual to Argyres-Douglas theories, present a puzzle as at first sight the symmetries do not match across the holographic correspondence. The spindle solutions, on the other hand, completely lack a proper understanding of their dual field theories.
This talk aims to shed light on these puzzles, offering a detailed explanation for the breaking of the unwanted symmetry in disc solution. Furthermore, we will clarify various aspects of the spindle solution, contributing to a more profound understanding of the class S origin of the dual SCFTs.
As a byproduct, we enlarge the class of holographic surface defects of the (2,0) theory as well as provide a concrete description of a class of locally N=1 preserving punctures.
Posted by: IC2
Wed
31 Jan 2024
Many-Particle Physics in QFT
📍 London
Matthew Walters
(Heriot-Watt U.)
Abstract:
I will discuss the physics of high energy, many-particle states from two complementary perspectives. First, I will present a new method for using data from conformal field theories to compute observables in more general QFTs, which can be used to numerically study many properties of many-particle states. Then I will consider an analytic approach to a particular set of these states, those near threshold, where many features become largely theory-independent.
I will discuss the physics of high energy, many-particle states from two complementary perspectives. First, I will present a new method for using data from conformal field theories to compute observables in more general QFTs, which can be used to numerically study many properties of many-particle states. Then I will consider an analytic approach to a particular set of these states, those near threshold, where many features become largely theory-independent.
Posted by: andrea
Mon
29 Jan 2024
Lonti: CFTs in Lorentzian signature (1/4)
Petr Kravchuk
(King's)
Abstract:
In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.
In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.
Posted by: andrea
Mon
29 Jan 2024
Defect two-point functions in 6d (2,0) theories
📍 London
Xinan Zhou
(Beijing, GUCAS)
Abstract:
In this talk, I will discuss correlation functions in 6d (2, 0) theories of two 1/2-BPS operators inserted away from a 1/2-BPS surface defect. In the large central charge limit the leading connected contribution corresponds to sums of tree-level Witten diagram in AdS7×S4 in the presence of an AdS3 defect. I will show that these correlators can be uniquely determined by imposing only superconformal symmetry and consistency conditions, eschewing the details of the complicated effective Lagrangian. I will present the explicit result of all such two-point functions, which exhibits remarkable hidden simplicity.
In this talk, I will discuss correlation functions in 6d (2, 0) theories of two 1/2-BPS operators inserted away from a 1/2-BPS surface defect. In the large central charge limit the leading connected contribution corresponds to sums of tree-level Witten diagram in AdS7×S4 in the presence of an AdS3 defect. I will show that these correlators can be uniquely determined by imposing only superconformal symmetry and consistency conditions, eschewing the details of the complicated effective Lagrangian. I will present the explicit result of all such two-point functions, which exhibits remarkable hidden simplicity.
Posted by: andrea
Fri
26 Jan 2024
Constructing polylogarithms on higher-genus Riemann surfaces
📍 London
Oliver Schlotterer
(Uppsala U.)
Abstract:
Recent developments on Feynman integrals and string amplitudes greatly benefitted from multiple polylogarithms and their elliptic analogues — iterated integrals on the sphere and the torus, respectively. In this talk, I will review the Brown-Levin construction of elliptic polylogarithms and propose a generalization to Riemann surfaces of arbitrary genus. In particular, iterated integrals on a higher-genus surface will be derived from a flat connection. The integration kernels of our flat connection consist of modular tensors, built from convolutions of Arakelov Green functions and their derivatives with holomorphic Abelian differentials. At genus one, these convolutions reproduce the Kronecker-Eisenstein kernels of elliptic polylogarithms and modular graph forms. I will conclude with an outlook on open problems and work in progress.
Recent developments on Feynman integrals and string amplitudes greatly benefitted from multiple polylogarithms and their elliptic analogues — iterated integrals on the sphere and the torus, respectively. In this talk, I will review the Brown-Levin construction of elliptic polylogarithms and propose a generalization to Riemann surfaces of arbitrary genus. In particular, iterated integrals on a higher-genus surface will be derived from a flat connection. The integration kernels of our flat connection consist of modular tensors, built from convolutions of Arakelov Green functions and their derivatives with holomorphic Abelian differentials. At genus one, these convolutions reproduce the Kronecker-Eisenstein kernels of elliptic polylogarithms and modular graph forms. I will conclude with an outlook on open problems and work in progress.
Posted by: QMW
Thu
25 Jan 2024
Trace Anomalies, RG Flow and Scattering Amplitudes
📍 London
Biswajit Sahoo
(King's College)
Abstract:
I will describe how various vertices and scattering amplitudes, involving background fields, probe trace anomaly coefficients in a four-dimensional (4D) renormalization group (RG) flow. Specifically, I will explain how to couple dilaton and graviton fields to the degrees of freedom of 4D QFT, ensuring the conservation of the Weyl anomaly along the RG flow for the coupled system. By providing dynamics to the dilaton and graviton fields, I will demonstrate that the graviton-dilaton scattering amplitude receives a universal contribution, exhibiting helicity flipping and being proportional to (Δc−Δa) along any RG flow. Here, Δc and Δa represent the differences in the UV and IR CFT c- and a-trace anomalies, respectively. Using a dispersion relation, (Δc−Δa) can be related to spinning massive states in the spectrum of the QFT. We test our proposal through various perturbative examples. Finally, as an application of the proposal of probing the trace anomalies using scattering amplitude, we have derived a non-perturbative bound on the UV CFT a-anomaly coefficient using numerical S-matrix bootstrap program for massive RG flow.
I will describe how various vertices and scattering amplitudes, involving background fields, probe trace anomaly coefficients in a four-dimensional (4D) renormalization group (RG) flow. Specifically, I will explain how to couple dilaton and graviton fields to the degrees of freedom of 4D QFT, ensuring the conservation of the Weyl anomaly along the RG flow for the coupled system. By providing dynamics to the dilaton and graviton fields, I will demonstrate that the graviton-dilaton scattering amplitude receives a universal contribution, exhibiting helicity flipping and being proportional to (Δc−Δa) along any RG flow. Here, Δc and Δa represent the differences in the UV and IR CFT c- and a-trace anomalies, respectively. Using a dispersion relation, (Δc−Δa) can be related to spinning massive states in the spectrum of the QFT. We test our proposal through various perturbative examples. Finally, as an application of the proposal of probing the trace anomalies using scattering amplitude, we have derived a non-perturbative bound on the UV CFT a-anomaly coefficient using numerical S-matrix bootstrap program for massive RG flow.
Posted by: QMW
Wed
24 Jan 2024
Entanglement and the classification and simulation of many-qubit systems
📍 London
Curt von Keyserlingk
(King's College London)
Abstract:
In recent years we've greatly expanded our understanding of entanglement in many-body quantum systems; both how it behaves in ground states, and how it grows out-of-equilibrium. While entanglement is very difficult to measure in experiments, it has nevertheless driven progress in 1) the classification of quantum phases of matter and 2) strategies for efficiently simulating many-body systems on classical and quantum computers. I will review some recent progress in these directions. Along the way I will summarise some older results on how entanglement grows in many-body systems, briefly highlight some connections to holography, and present a conjecture about the asymptotic computational difficulty of calculating transport in many-body systems.
In recent years we've greatly expanded our understanding of entanglement in many-body quantum systems; both how it behaves in ground states, and how it grows out-of-equilibrium. While entanglement is very difficult to measure in experiments, it has nevertheless driven progress in 1) the classification of quantum phases of matter and 2) strategies for efficiently simulating many-body systems on classical and quantum computers. I will review some recent progress in these directions. Along the way I will summarise some older results on how entanglement grows in many-body systems, briefly highlight some connections to holography, and present a conjecture about the asymptotic computational difficulty of calculating transport in many-body systems.
Posted by: andrea
Wed
24 Jan 2024
Probing the deep string spectrum
Chrysoula MARKOU
(University of Mons)
Abstract:
As is well known, the string spectrum comprises infinitely many states that can collectively be visualized along Regge trajectories of increasing mass and spin. Its massless and lightest levels, as well as certain higher spins including the leading Regge trajectory, have been the focus of past studies. In principle, access to any state is possible, but the traditional methodology is non-covariant and does not immediately lead to irreducible representations of the Wigner little group. In this talk, we will discuss a new and covariant technology of constructing the string spectrum. It is based on the observation that there is a bigger symmetry behind the Virasoro constraints: the symplectic algebra that commutes with the spacetime Lorenz algebra. This enables excavating string states and their interactions by entire trajectories, rather than individually.
As is well known, the string spectrum comprises infinitely many states that can collectively be visualized along Regge trajectories of increasing mass and spin. Its massless and lightest levels, as well as certain higher spins including the leading Regge trajectory, have been the focus of past studies. In principle, access to any state is possible, but the traditional methodology is non-covariant and does not immediately lead to irreducible representations of the Wigner little group. In this talk, we will discuss a new and covariant technology of constructing the string spectrum. It is based on the observation that there is a bigger symmetry behind the Virasoro constraints: the symplectic algebra that commutes with the spacetime Lorenz algebra. This enables excavating string states and their interactions by entire trajectories, rather than individually.
Posted by: IC2
Wed
24 Jan 2024
TBA
📍 London
Curt von Keyserlingk
(King's College London)
Thu
18 Jan 2024
Gravitational Waves from Worldline Quantum Field Theory
📍 London
Gustav Mogull
(Humboldt U.)
Abstract:
I will discuss our recent calculations of the observables involved in the scattering of two black holes or neutron stars at fourth post-Minkowskian order (three loops) using the Worldline Quantum Field Theory (WQFT) framework. These 4PM observables now include both spin-orbit and adiabatic tidal corrections — inclusion of the latter necessitates a renormalization of the underlying classical effective field theory (EFT). I will also explain how the Effective-One-Body (EOB) may be used to resum the observables, and provide input data for future-generation gravitational waveform models.
I will discuss our recent calculations of the observables involved in the scattering of two black holes or neutron stars at fourth post-Minkowskian order (three loops) using the Worldline Quantum Field Theory (WQFT) framework. These 4PM observables now include both spin-orbit and adiabatic tidal corrections — inclusion of the latter necessitates a renormalization of the underlying classical effective field theory (EFT). I will also explain how the Effective-One-Body (EOB) may be used to resum the observables, and provide input data for future-generation gravitational waveform models.
Posted by: QMW
Mon
15 Jan 2024
Some Aspects of Krylov Complexity
Eliezer Rabinovici
(Hebrew University of Jerusalem)
Abstract:
A review of the concept of Krylov Complexity(K- Complexity) will be presented. One feature of K-Complexity is that its definition does not involve a tolerance parameter. I will describe some general properties of K-Complexity, its behavior when interpolating among various types of systems: free, strongly integrable and chaotic ones. Finally for a certain low dimensional system in a certain state I will describe an explicit derivation of the geometric bulk dual of K complexity.
A review of the concept of Krylov Complexity(K- Complexity) will be presented. One feature of K-Complexity is that its definition does not involve a tolerance parameter. I will describe some general properties of K-Complexity, its behavior when interpolating among various types of systems: free, strongly integrable and chaotic ones. Finally for a certain low dimensional system in a certain state I will describe an explicit derivation of the geometric bulk dual of K complexity.
Posted by: IC2