Triangle Seminars
June 2025
Fri
13 Jun 2025
Black hole cohomologies at finite N
📍 London
Sunjin Choi
(IPMU)
Abstract:
We study new cohomologies for the local BPS operators of the maximal super-Yang-Mills theory to better understand the black hole microstates. We first analyze the index of these black hole operators, and explicitly construct their cohomologies to study how they imitate the quantum black holes. We find many towers of states and partial no-hair behaviors, where certain gravtions are forbidden to dress these black hole operators. This qualitatively agrees with the behavior of the perturbative hairy BPS black holes or the so-called grey galaxies. Throughout this talk, we mainly focus on a subsector of the field theory corresponding to the BMN matrix theory, which exhibits a black hole-like entropy growth at large N.
We study new cohomologies for the local BPS operators of the maximal super-Yang-Mills theory to better understand the black hole microstates. We first analyze the index of these black hole operators, and explicitly construct their cohomologies to study how they imitate the quantum black holes. We find many towers of states and partial no-hair behaviors, where certain gravtions are forbidden to dress these black hole operators. This qualitatively agrees with the behavior of the perturbative hairy BPS black holes or the so-called grey galaxies. Throughout this talk, we mainly focus on a subsector of the field theory corresponding to the BMN matrix theory, which exhibits a black hole-like entropy growth at large N.
Posted by: QMW
Wed
11 Jun 2025
Disturbing news about the 2+epsilon expansion
Fabiana Cesare
(IHES)
Abstract:
The O(N) Non-Linear Sigma Model (NLSM) in d=2+epsilon has long been conjectured to describe the same conformal field theory as the Wilson-Fisher O(N) fixed point obtained from the (phi^2)^2 model in
d=4-epsilon. In this talk, we put this conjecture into question, building on the recent observation [Jones,2024] that the NLSM CFT possesses a protected operator with dimension N-1, which is instead absent in the WF O(N) CFT. We propose several scenarios that may explain this discrepancy.
The O(N) Non-Linear Sigma Model (NLSM) in d=2+epsilon has long been conjectured to describe the same conformal field theory as the Wilson-Fisher O(N) fixed point obtained from the (phi^2)^2 model in
d=4-epsilon. In this talk, we put this conjecture into question, building on the recent observation [Jones,2024] that the NLSM CFT possesses a protected operator with dimension N-1, which is instead absent in the WF O(N) CFT. We propose several scenarios that may explain this discrepancy.
Posted by: IC2
Wed
11 Jun 2025
Spin Matrix theory and SU(1,n) type of holography in N=4 SYM
📍 London
Yang Lei
(Soochow University)
Abstract:
The Spin Matrix theory is the non-relativistic decoupled limit of N=4 SYM, capturing the near BPS dynamics of N=4 SYM. In this talk I will review the construction of Spin Matrix theory I have been doing in the past few years, following 2012.08532, 2111.10149, 2211.16519. These models could also be viewed as models of holography with SU(1,1) and SU(1,2) type of symmetry. As a nontrivial generalization of Lorentzian type of theories, we will discuss the state-operator correspondence in SU(1,2) type CFT.
The Spin Matrix theory is the non-relativistic decoupled limit of N=4 SYM, capturing the near BPS dynamics of N=4 SYM. In this talk I will review the construction of Spin Matrix theory I have been doing in the past few years, following 2012.08532, 2111.10149, 2211.16519. These models could also be viewed as models of holography with SU(1,1) and SU(1,2) type of symmetry. As a nontrivial generalization of Lorentzian type of theories, we will discuss the state-operator correspondence in SU(1,2) type CFT.
Posted by: QMW
Mon
9 Jun 2025
Lonti: Superstring Perturbation Theory (4/4)
📍 London
Ashoke Sen
(ICTS, Bangalore)
Abstract:
Please register at https://forms.gle/pHFLVU2XeZu39gzVA
The world-sheet CFT for bosonic string theory, matter and ghost system, BRST charge, physical state condition
Definition of higher genus Riemann surfaces, defining CFT correlations on higher genus Riemann surfaces, bosonic string amplitudes at any loop order
Heterotic and superstring theory, world-sheet CFT of matter and ghosts, picture number and picture changing operator, superstring amplitude at any loop order
Vertical integration and removal of spurious divergences
Please register at https://forms.gle/pHFLVU2XeZu39gzVA
The world-sheet CFT for bosonic string theory, matter and ghost system, BRST charge, physical state condition
Definition of higher genus Riemann surfaces, defining CFT correlations on higher genus Riemann surfaces, bosonic string amplitudes at any loop order
Heterotic and superstring theory, world-sheet CFT of matter and ghosts, picture number and picture changing operator, superstring amplitude at any loop order
Vertical integration and removal of spurious divergences
Posted by: andrea
Thu
5 Jun 2025
Carroll Approximations of General Relativity, BKL Dynamics and Holography
📍 London
Gerben Oling
(Edinburgh U., Sch. Math.)
Abstract:
What goes on behind the horizon of black holes? A long time ago, general relativity was conjectured to lead to chaotic dynamics in the vicinity of spacelike singularities. Recently, it was observed that this so-called BKL dynamics, which features 'bounces' between Kasner geometries, can be engineered in AdS black holes in a relatively straightforward way using relevant deformations in the dual CFT. However, extracting predictions from Einstein gravity in this near-singularity regime remains extraordinarily challenging, which limits our understanding of the validity and generality of BKL limits as well as their holographic interpretation in AdS/CFT. In this talk, I will present a novel approach to the challenges of near-singularity dynamics and its holographic interpretation using ultra-local geometric Carroll approximations of gravity.
What goes on behind the horizon of black holes? A long time ago, general relativity was conjectured to lead to chaotic dynamics in the vicinity of spacelike singularities. Recently, it was observed that this so-called BKL dynamics, which features 'bounces' between Kasner geometries, can be engineered in AdS black holes in a relatively straightforward way using relevant deformations in the dual CFT. However, extracting predictions from Einstein gravity in this near-singularity regime remains extraordinarily challenging, which limits our understanding of the validity and generality of BKL limits as well as their holographic interpretation in AdS/CFT. In this talk, I will present a novel approach to the challenges of near-singularity dynamics and its holographic interpretation using ultra-local geometric Carroll approximations of gravity.
Posted by: QMW
Thu
5 Jun 2025
Classical Gravitational Wave Tails from Soft Theorem
📍 London
Ashoke Sen
(ICTS, Bangalore)
Abstract:
If a set of massive objects collide in space and the fragments disperse, possibly forming black holes, then this process will emit gravitational waves. Computing the detailed gravitational wave-form associated with this process is a complicated problem, not only due to the non-linearity of gravity but also due to the fact that during the collision and subsequent fragmentation the objects could undergo complicated non-gravitational interactions. Nevertheless the classical soft graviton theorem determines the power law fall-off of the wave-form at late and early times, including logarithmic corrections, in terms of only the momenta of the incoming and outgoing objects without any reference to what transpired during the collision. I shall explain the results, briefly outline the derivation of these results and discuss possible generalizations and applications.
The talk will be followed by a reception in Bush House (SE) 2.12. Participation is free, but external attendees are asked to register on https://www.eventbrite.co.uk/e/mathematics-colloquiaclassical-gravitational-wave-tails-from-soft-theorem-tickets-1354870717789?aff=oddtdtcreator.
If a set of massive objects collide in space and the fragments disperse, possibly forming black holes, then this process will emit gravitational waves. Computing the detailed gravitational wave-form associated with this process is a complicated problem, not only due to the non-linearity of gravity but also due to the fact that during the collision and subsequent fragmentation the objects could undergo complicated non-gravitational interactions. Nevertheless the classical soft graviton theorem determines the power law fall-off of the wave-form at late and early times, including logarithmic corrections, in terms of only the momenta of the incoming and outgoing objects without any reference to what transpired during the collision. I shall explain the results, briefly outline the derivation of these results and discuss possible generalizations and applications.
The talk will be followed by a reception in Bush House (SE) 2.12. Participation is free, but external attendees are asked to register on https://www.eventbrite.co.uk/e/mathematics-colloquiaclassical-gravitational-wave-tails-from-soft-theorem-tickets-1354870717789?aff=oddtdtcreator.
Posted by: andrea
Thu
5 Jun 2025
Why Nobody Understands Quantum Physics
Frank Verstraete
(Cambridge U)
Abstract:
Prof. Frank Verstraete and Celine Broeckaert invite you to a talk celebrating 100 years of quantum and the launch of their book: Why Nobody Understands Quantum Physics. The talk is at the Royal Institution (21 Albemarle St, London W1S 4BS). Please RSVP at RSVPEVENTS_at_MACMILLAN.COM.
Prof. Frank Verstraete and Celine Broeckaert invite you to a talk celebrating 100 years of quantum and the launch of their book: Why Nobody Understands Quantum Physics. The talk is at the Royal Institution (21 Albemarle St, London W1S 4BS). Please RSVP at RSVPEVENTS_at_MACMILLAN.COM.
Posted by: QMW
Mon
2 Jun 2025
Lonti: Superstring Perturbation Theory (3/4)
📍 London
Ashoke Sen
(ICTS, Bangalore)
Abstract:
Please register at https://forms.gle/pHFLVU2XeZu39gzVA
The world-sheet CFT for bosonic string theory, matter and ghost system, BRST charge, physical state condition
Definition of higher genus Riemann surfaces, defining CFT correlations on higher genus Riemann surfaces, bosonic string amplitudes at any loop order
Heterotic and superstring theory, world-sheet CFT of matter and ghosts, picture number and picture changing operator, superstring amplitude at any loop order
Vertical integration and removal of spurious divergences
Please register at https://forms.gle/pHFLVU2XeZu39gzVA
The world-sheet CFT for bosonic string theory, matter and ghost system, BRST charge, physical state condition
Definition of higher genus Riemann surfaces, defining CFT correlations on higher genus Riemann surfaces, bosonic string amplitudes at any loop order
Heterotic and superstring theory, world-sheet CFT of matter and ghosts, picture number and picture changing operator, superstring amplitude at any loop order
Vertical integration and removal of spurious divergences
Posted by: andrea
May 2025
Fri
30 May 2025
Lonti: Superstring Perturbation Theory (2/4)
Ashoke Sen
(ICTS, Bangalore)
Abstract:
Please register at https://forms.gle/pHFLVU2XeZu39gzVA
The world-sheet CFT for bosonic string theory, matter and ghost system, BRST charge, physical state condition
Definition of higher genus Riemann surfaces, defining CFT correlations on higher genus Riemann surfaces, bosonic string amplitudes at any loop order
Heterotic and superstring theory, world-sheet CFT of matter and ghosts, picture number and picture changing operator, superstring amplitude at any loop order
Vertical integration and removal of spurious divergences
Please register at https://forms.gle/pHFLVU2XeZu39gzVA
The world-sheet CFT for bosonic string theory, matter and ghost system, BRST charge, physical state condition
Definition of higher genus Riemann surfaces, defining CFT correlations on higher genus Riemann surfaces, bosonic string amplitudes at any loop order
Heterotic and superstring theory, world-sheet CFT of matter and ghosts, picture number and picture changing operator, superstring amplitude at any loop order
Vertical integration and removal of spurious divergences
Posted by: andrea
Thu
29 May 2025
de Sitter Space as a coherent state
📍 London
Radu Tatar
(university of Liverpool)
Abstract:
We consider an M theory/string theory approach to support the fact that a four-dimensional effective field theory description with de Sitter isometries can exist if de Sitter space is realised as a coherent state.
We consider an M theory/string theory approach to support the fact that a four-dimensional effective field theory description with de Sitter isometries can exist if de Sitter space is realised as a coherent state.
Posted by: QMW
Thu
29 May 2025
Dialogues on AI and Science
Michael Douglas
(Harvard)
Abstract:
informal seminar and dialogues with Mike in our historical rooms.
informal seminar and dialogues with Mike in our historical rooms.
Posted by: oxford
Thu
29 May 2025
Cosmological correlators in gravitationally constrained de Sitter states
📍 London
Tuneer Chakraborty
(Tata Institute of Fundamental Research (TIFR), Mumbai)
Abstract:
We study perturbative cosmological correlators in wavefunctionals which solve the Wheeler-DeWitt equation in asymptotically de Sitter spacetimes and were constructed in arxiv:2303.16315. Even in the G_N -> 0 limit, it is necessary to impose the gravitational Gauss law, which forces states to be de Sitter invariant. We set up Feynman rules for computing cosmological correlators in such states. We enumerate some necessary (but not sufficient) conditions that must be imposed on states and observables to avoid group-volume divergences. We provide sample computations to show that such cosmological correlators can be nontrivial even when the Hartle-Hawking wavefunction is Gaussian. We show that, in the presence of a heavy background state, it is possible to construct a class of state-dependent relational observables that approximate correlators in the Hartle-Hawking state.
We study perturbative cosmological correlators in wavefunctionals which solve the Wheeler-DeWitt equation in asymptotically de Sitter spacetimes and were constructed in arxiv:2303.16315. Even in the G_N -> 0 limit, it is necessary to impose the gravitational Gauss law, which forces states to be de Sitter invariant. We set up Feynman rules for computing cosmological correlators in such states. We enumerate some necessary (but not sufficient) conditions that must be imposed on states and observables to avoid group-volume divergences. We provide sample computations to show that such cosmological correlators can be nontrivial even when the Hartle-Hawking wavefunction is Gaussian. We show that, in the presence of a heavy background state, it is possible to construct a class of state-dependent relational observables that approximate correlators in the Hartle-Hawking state.
Posted by: QMW
Tue
27 May 2025
Lonti: Superstring Perturbation Theory (1/4)
Ashoke Sen
(ICTS, Bangalore)
Abstract:
Please register at https://forms.gle/pHFLVU2XeZu39gzVA
The world-sheet CFT for bosonic string theory, matter and ghost system, BRST charge, physical state condition
Definition of higher genus Riemann surfaces, defining CFT correlations on higher genus Riemann surfaces, bosonic string amplitudes at any loop order
Heterotic and superstring theory, world-sheet CFT of matter and ghosts, picture number and picture changing operator, superstring amplitude at any loop order
Vertical integration and removal of spurious divergences
Please register at https://forms.gle/pHFLVU2XeZu39gzVA
The world-sheet CFT for bosonic string theory, matter and ghost system, BRST charge, physical state condition
Definition of higher genus Riemann surfaces, defining CFT correlations on higher genus Riemann surfaces, bosonic string amplitudes at any loop order
Heterotic and superstring theory, world-sheet CFT of matter and ghosts, picture number and picture changing operator, superstring amplitude at any loop order
Vertical integration and removal of spurious divergences
Posted by: andrea
Tue
27 May 2025
Uplifting Massive Graphs from Minkowski to de Sitter
📍 London
Sadra Jazayeri
(Imperial College London)
Abstract:
Identifying useful flat-space limits of cosmological correlators defined on the future boundary of de Sitter space is challenging due to their inherent scale invariance. In this talk, I present a massive flat-space limit in which cosmological correlators arising from the exchange of heavy fields can be expressed in terms of massive Feynman diagrams in Minkowski space. As a phenomenological application, I use this limit to compute the imprints of massive particles during inflation on primordial non-Gaussianity. These results offer new channels for discovering inflation-era particles with the next generation of CMB and large-scale structure surveys, such as Simons Observatory and SPHEREx.
Identifying useful flat-space limits of cosmological correlators defined on the future boundary of de Sitter space is challenging due to their inherent scale invariance. In this talk, I present a massive flat-space limit in which cosmological correlators arising from the exchange of heavy fields can be expressed in terms of massive Feynman diagrams in Minkowski space. As a phenomenological application, I use this limit to compute the imprints of massive particles during inflation on primordial non-Gaussianity. These results offer new channels for discovering inflation-era particles with the next generation of CMB and large-scale structure surveys, such as Simons Observatory and SPHEREx.
Posted by: QMUL2
Wed
21 May 2025
D-instanton amplitudes in string theory
Ashoke Sen
(ICTS, Bangalore)
Abstract:
D-instantons give non-perturbative contribution to string amplitudes. While world-sheet theory gives a formal expression for these amplitudes, they are often divergent. We review how string field theory can be used to systematically extract unambiguous, finite results from these divergent expressions.
D-instantons give non-perturbative contribution to string amplitudes. While world-sheet theory gives a formal expression for these amplitudes, they are often divergent. We review how string field theory can be used to systematically extract unambiguous, finite results from these divergent expressions.
Posted by: IC2
Wed
21 May 2025
Are moduli vacuum expectation values or parameters?
Ashoke Sen
(ICTS, Bangalore)
Abstract:
In a quantum field theory moduli are scalar fields without potentials and we define the quantum field theory for fixed asymptotic values of the moduli. Yet once we know all the observables for some fixed asymptotic values of the moduli, they contain complete information on the observables for any other asymptotic values of the moduli. The situation in a quantum theory of gravity is more complicated. We review these issues, describe the essential difference between quantum gravity in flat space-time and AdS space-time and the implications of these observations for possible holographic dual of string theory in flat space-time.
In a quantum field theory moduli are scalar fields without potentials and we define the quantum field theory for fixed asymptotic values of the moduli. Yet once we know all the observables for some fixed asymptotic values of the moduli, they contain complete information on the observables for any other asymptotic values of the moduli. The situation in a quantum theory of gravity is more complicated. We review these issues, describe the essential difference between quantum gravity in flat space-time and AdS space-time and the implications of these observations for possible holographic dual of string theory in flat space-time.
Posted by: IC2
Thu
15 May 2025
Models of AdS Black Holes from Free CFT Duals
📍 London
Bo Sundborg
(Stockholm University)
Abstract:
The AdS/CFT correspondence permits the study of bulk duals to free CFTs with gauge symmetries, such as U(N) with large N. In free models CFT correlators are explicitly known. Thermal observables reveal a black hole-like character of massive bulk objects, indicating that classical spacetime emerges by assuming large N in free theories, while strong coupling of the boundary theory is mainly significant quantitatively. I review the origins and the evidence for the above assertions, with future developments in mind. In general, it is important to consider finite but large N to capture non-perturbative gravity effects.
The AdS/CFT correspondence permits the study of bulk duals to free CFTs with gauge symmetries, such as U(N) with large N. In free models CFT correlators are explicitly known. Thermal observables reveal a black hole-like character of massive bulk objects, indicating that classical spacetime emerges by assuming large N in free theories, while strong coupling of the boundary theory is mainly significant quantitatively. I review the origins and the evidence for the above assertions, with future developments in mind. In general, it is important to consider finite but large N to capture non-perturbative gravity effects.
Posted by: QMW
Thu
15 May 2025
String Theory and the First Half of the Universe
Joseph Conlon
(Oxford)
Abstract:
The period between inflation and nucleosynthesis can last for thirty orders of magnitude of time and represent half the lifetime of the universe on a logarithmic scale. But yet, there are minimal observational constraints on this epoch. String cosmologies motivate a rich set of modifications from the standard radiation-dominated post-inflationary assumption of Lambda CDM. In particular, string cosmology suggests the likelihood of moduli-dominated cosmologies through kination, tracker and matter epochs. I review the possible scenarios and observational possibilities, including a novel percolation scenario for formation of cosmic string networks.
The period between inflation and nucleosynthesis can last for thirty orders of magnitude of time and represent half the lifetime of the universe on a logarithmic scale. But yet, there are minimal observational constraints on this epoch. String cosmologies motivate a rich set of modifications from the standard radiation-dominated post-inflationary assumption of Lambda CDM. In particular, string cosmology suggests the likelihood of moduli-dominated cosmologies through kination, tracker and matter epochs. I review the possible scenarios and observational possibilities, including a novel percolation scenario for formation of cosmic string networks.
Posted by: oxford
Wed
14 May 2025
Solving N=2 superconformal long-quiver theories with Tracy-Widom distributions
Alessandro Testa
(Universita di Parma and INFN)
Abstract:
In this seminar, I will discuss two- and three-point correlation functions of chiral primary half-BPS operators in four-dimensional \(\mathcal{N}=2\) superconformal circular, cyclic symmetric quiver theories. Using supersymmetric localization, these functions can be expressed as matrix integrals which, in the planar limit, reduce to Fredholm determinants of certain semi-infinite matrices. This powerful representation allows us to investigate the correlation functions across the parameter space of the quiver theory, including both weak and strong coupling regimes and various limits of the number of nodes and the operator scaling dimensions. At strong coupling, the standard semiclassical AdS/CFT expansion diverges in the long quiver limit. However, by incorporating both perturbative corrections (in negative powers of the 't Hooft coupling) and an infinite tower of nonperturbative, exponentially suppressed contributions, we derive a remarkably simple expression for the correlation functions in this limit.These functions exhibit exponential decay with increasing node separation and admit an interpretation within a five-dimensional effective theory.We determine the mass spectrum of excitations propagating along the emergent fifth dimension within this theory, finding it to be given by the zeros of Bessel functions.
In this seminar, I will discuss two- and three-point correlation functions of chiral primary half-BPS operators in four-dimensional \(\mathcal{N}=2\) superconformal circular, cyclic symmetric quiver theories. Using supersymmetric localization, these functions can be expressed as matrix integrals which, in the planar limit, reduce to Fredholm determinants of certain semi-infinite matrices. This powerful representation allows us to investigate the correlation functions across the parameter space of the quiver theory, including both weak and strong coupling regimes and various limits of the number of nodes and the operator scaling dimensions. At strong coupling, the standard semiclassical AdS/CFT expansion diverges in the long quiver limit. However, by incorporating both perturbative corrections (in negative powers of the 't Hooft coupling) and an infinite tower of nonperturbative, exponentially suppressed contributions, we derive a remarkably simple expression for the correlation functions in this limit.These functions exhibit exponential decay with increasing node separation and admit an interpretation within a five-dimensional effective theory.We determine the mass spectrum of excitations propagating along the emergent fifth dimension within this theory, finding it to be given by the zeros of Bessel functions.
Posted by: IC2
Wed
14 May 2025
TBA
📍 London
Bernardo Zan
(University of Genoa)
Fri
9 May 2025
A Universal Connection Between 3d N=4 SCFTs and 3d TQFTs
Matthew Buican
(Queen Mary University of London)
Abstract:
I will describe work on a universal relevant deformation that takes local unitary 3d N=4 superconformal field theories to topological quantum field theories. For example, I will describe how Abelian mirror symmetry is related to generalizations of level rank duality, and I will also discuss some more general statements and constraints that arise via t Hooft anomaly matching.
I will describe work on a universal relevant deformation that takes local unitary 3d N=4 superconformal field theories to topological quantum field theories. For example, I will describe how Abelian mirror symmetry is related to generalizations of level rank duality, and I will also discuss some more general statements and constraints that arise via t Hooft anomaly matching.
Posted by: oxford
Thu
8 May 2025
Interpolating indices in superconformal N=2 gauge theories in four dimensions
📍 London
Itamar Yaakov
(University of Southampton)
Abstract:
I will discuss work in preparation which relates two quantities in 4d N=2 supersymmetric theories: the superconformal index, which contains information about protected local operators, and the twisted index. I will show that under appropriate restrictions on the theory and the space of supersymmetric deformations, these quantities coincide. I will then discuss some implications for the physics of the theory and its holographic dual.
I will discuss work in preparation which relates two quantities in 4d N=2 supersymmetric theories: the superconformal index, which contains information about protected local operators, and the twisted index. I will show that under appropriate restrictions on the theory and the space of supersymmetric deformations, these quantities coincide. I will then discuss some implications for the physics of the theory and its holographic dual.
Posted by: QMW
Wed
7 May 2025
Where is tree-level string theory?
📍 London
Leonardo Rastelli
(Stony Brook U.)
Abstract:
Tree-level string theory extends Einstein gravity by an infinite set of massive higher spin particles. From a purely spacetime perspective (if we didn't know about the worldsheet picture) the consistency of string amplitudes would appear truly miraculous. This prompts the question: is string theory the unique framework for a higher spin extension of gravity? We investigate this question by bootstrap methods, focussing on maximal 10D supergravity. We parametrize theory space by the first few EFT coefficients and by the on-shell coupling of the lightest massive state, and impose on these data causality and positivity constraints. While Type II string theory lives strictly inside the allowed region, we uncover a novel extremal solution of the bootstrap problem, which appears to contain a single linear Regge trajectory. We repeat a similar analysis for supergluon scattering.
Tree-level string theory extends Einstein gravity by an infinite set of massive higher spin particles. From a purely spacetime perspective (if we didn't know about the worldsheet picture) the consistency of string amplitudes would appear truly miraculous. This prompts the question: is string theory the unique framework for a higher spin extension of gravity? We investigate this question by bootstrap methods, focussing on maximal 10D supergravity. We parametrize theory space by the first few EFT coefficients and by the on-shell coupling of the lightest massive state, and impose on these data causality and positivity constraints. While Type II string theory lives strictly inside the allowed region, we uncover a novel extremal solution of the bootstrap problem, which appears to contain a single linear Regge trajectory. We repeat a similar analysis for supergluon scattering.
Posted by: andrea
Thu
1 May 2025
Interacting Fields at Spatial Infinity
📍 London
Priyadarshi Paul
(Queen Mary University of London)
Abstract:
We study the properties of massive fields extrapolated to the blowup of spatial infinity (\hat{i}^0), extending the program initiated in arXiv:2207.06406. Although the motivation is to understand holography in the quantum theory of gravity for asymptotically flat spacetime, in this work we do not include dynamical gravity. Instead, we focus on understanding boundary operators in the fixed background for free as well as interacting theory. In the free theory, we find an explicit representation of boundary two-point functions and boundary-to-bulk two-point functions. We also present an HKLL-type reconstruction formula for local bulk operators in terms of smeared boundary operators. We study interacting Wightman correlators and find that, generically, interacting massive fields decay slower than free fields as one approaches \hat{i}^0. We propose that meaningful correlators at \hat{i}^0 can be obtained through an LSZ-like prescription that isolates the on-shell part of bulk Wightman correlators before extrapolating them to \hat{i}^0. We show that a natural basis for operators at \hat{i}^0, defined via this prescription, is given by the average of "in" and "out" operators defined at i^− and i^+ respectively. Therefore, correlators at \hat{i}^0 and cross correlators between \hat{i}^0, i^− and i^+ can be represented within the class of asymptotic observables studied by Caron-Huot et al. in arXiv:2308.02125. We present several sample calculations. In the future, we plan to couple dynamical gravity to the theory and see how it helps us understand holography.
We study the properties of massive fields extrapolated to the blowup of spatial infinity (\hat{i}^0), extending the program initiated in arXiv:2207.06406. Although the motivation is to understand holography in the quantum theory of gravity for asymptotically flat spacetime, in this work we do not include dynamical gravity. Instead, we focus on understanding boundary operators in the fixed background for free as well as interacting theory. In the free theory, we find an explicit representation of boundary two-point functions and boundary-to-bulk two-point functions. We also present an HKLL-type reconstruction formula for local bulk operators in terms of smeared boundary operators. We study interacting Wightman correlators and find that, generically, interacting massive fields decay slower than free fields as one approaches \hat{i}^0. We propose that meaningful correlators at \hat{i}^0 can be obtained through an LSZ-like prescription that isolates the on-shell part of bulk Wightman correlators before extrapolating them to \hat{i}^0. We show that a natural basis for operators at \hat{i}^0, defined via this prescription, is given by the average of "in" and "out" operators defined at i^− and i^+ respectively. Therefore, correlators at \hat{i}^0 and cross correlators between \hat{i}^0, i^− and i^+ can be represented within the class of asymptotic observables studied by Caron-Huot et al. in arXiv:2308.02125. We present several sample calculations. In the future, we plan to couple dynamical gravity to the theory and see how it helps us understand holography.
Posted by: QMW
April 2025
Thu
24 Apr 2025
Modern aspects of the black hole/string correspondence
📍 London
Marija Tomasevic
(Unversity of Amsterdam)
Abstract:
I will review the basic story behind the black hole/string correspondence, its advantages, and its limits. I will then summarize some recent progress on this topic and go over several possible open directions.
I will review the basic story behind the black hole/string correspondence, its advantages, and its limits. I will then summarize some recent progress on this topic and go over several possible open directions.
Posted by: QMW
Wed
23 Apr 2025
Old and new physics in the J1-J2 Heisenberg spin chain
📍 London
Chris Hooley
(Coventry)
Abstract:
In this talk, I will briefly describe two of our recent pieces of work on the physics of the J1-J2 Heisenberg spin chain, a one-dimensional array of quantum spins coupled by first- and second-neighbour exchange interactions. The first piece of work [1] concerns the case where J1 and J2 are both antiferromagnetic: in this case there is a phase transition from a Luttinger liquid to a valence bond solid as In this talk, I will briefly describe two of our recent pieces of work on the physics of the J1-J2 Heisenberg spin chain, a one-dimensional array of quantum spins coupled by first- and second-neighbour exchange interactions. The first piece of work [1] concerns the case where J1 and J2 are both antiferromagnetic: in this case there is a phase transition from a Luttinger liquid to a valence bond solid as J2/J1 In this talk, I will briefly describe two of our recent pieces of work on the physics of the J1-J2 Heisenberg spin chain, a one-dimensional array of quantum spins coupled by fi
rst- and second-neighbour exchange interactions. The first piece of work [1] concerns the case where J1 and J2 are both antiferromagnetic: in this case there is a phase transition from a Luttinger liquid to a valence bond solid as J2/J1 is increased, and we provide a novel direct method to derive the field theory that describes the critical point between these two phases. The second piece [2] concerns the case where J1 is antiferromagnetic but J2 is strongly ferromagnetic: counter-intuitively, there is a transition in this case as well, but this time of a "liquid-to-liquid" type. We present a field-theory description of it, and an analogue system of three coupled chains that helps to illustrate the physics.
[1] F. Azad, A. J. McRoberts, CAH, and A. G. Green, "Generalized Haldane map from the matrix product state path integral to the critical theory of the J1-J2 chain," Phys. Rev. Research 7, L012037 (2025).
[2] A. J. McRoberts, CAH, and A. G. Green, "Transition between critical antiferromagnetic phases in the J1-J2 spin chain," arXiv:2411.08095v2 (2025).
In this talk, I will briefly describe two of our recent pieces of work on the physics of the J1-J2 Heisenberg spin chain, a one-dimensional array of quantum spins coupled by first- and second-neighbour exchange interactions. The first piece of work [1] concerns the case where J1 and J2 are both antiferromagnetic: in this case there is a phase transition from a Luttinger liquid to a valence bond solid as In this talk, I will briefly describe two of our recent pieces of work on the physics of the J1-J2 Heisenberg spin chain, a one-dimensional array of quantum spins coupled by first- and second-neighbour exchange interactions. The first piece of work [1] concerns the case where J1 and J2 are both antiferromagnetic: in this case there is a phase transition from a Luttinger liquid to a valence bond solid as J2/J1 In this talk, I will briefly describe two of our recent pieces of work on the physics of the J1-J2 Heisenberg spin chain, a one-dimensional array of quantum spins coupled by fi
rst- and second-neighbour exchange interactions. The first piece of work [1] concerns the case where J1 and J2 are both antiferromagnetic: in this case there is a phase transition from a Luttinger liquid to a valence bond solid as J2/J1 is increased, and we provide a novel direct method to derive the field theory that describes the critical point between these two phases. The second piece [2] concerns the case where J1 is antiferromagnetic but J2 is strongly ferromagnetic: counter-intuitively, there is a transition in this case as well, but this time of a "liquid-to-liquid" type. We present a field-theory description of it, and an analogue system of three coupled chains that helps to illustrate the physics.
[1] F. Azad, A. J. McRoberts, CAH, and A. G. Green, "Generalized Haldane map from the matrix product state path integral to the critical theory of the J1-J2 chain," Phys. Rev. Research 7, L012037 (2025).
[2] A. J. McRoberts, CAH, and A. G. Green, "Transition between critical antiferromagnetic phases in the J1-J2 spin chain," arXiv:2411.08095v2 (2025).
Posted by: QMW
Thu
17 Apr 2025
5d Conformal Matter - Atoms, Molecules and Hybrids
📍 London
Julius Grimminger
(University of Oxford)
Abstract:
A recently introduced class of 5d superconformal field theories (SCFTs), dubbed 5d conformal matter (CM) in reference to the well known 6d CM theories, is constructed in M-theory on Calabi-Yau threefolds (CY3s) which can be viewed as intersecting ADE singularities. I will address the classification of these theories - based on the weight lattice of ADE algebras - which fall into three classes: Atoms, Molecules, and so called Hybrids. I will show how these three types are distinguished by their geometric construction. Further we will explore the brane constructions dual to the CY3s where possible, the quantum Higgs branch of the 5d CM theories, and the circle reduction to 4 dimensions.
A recently introduced class of 5d superconformal field theories (SCFTs), dubbed 5d conformal matter (CM) in reference to the well known 6d CM theories, is constructed in M-theory on Calabi-Yau threefolds (CY3s) which can be viewed as intersecting ADE singularities. I will address the classification of these theories - based on the weight lattice of ADE algebras - which fall into three classes: Atoms, Molecules, and so called Hybrids. I will show how these three types are distinguished by their geometric construction. Further we will explore the brane constructions dual to the CY3s where possible, the quantum Higgs branch of the 5d CM theories, and the circle reduction to 4 dimensions.
Posted by: QMW
Tue
15 Apr 2025
De Sitter quantum gravity and the emergence of local algebras
📍 London
Molly Kaplan
(Mines Paris - PSL)
Abstract:
Quantum theories of gravity are generally expected to have some degree of nonlocality, with familiar local physics emerging only in a particular limit. Perturbative quantum gravity around backgrounds with isometries and compact Cauchy slices provides an interesting laboratory in which this emergence can be explored. In this context, the remaining isometries are gauge symmetries and, as a result, gauge-invariant observables cannot be localized. Instead, local physics can arise only through certain relational constructions. In this talk, we explore such issues for perturbative quantum gravity around de Sitter space. In particular, we describe a class of gauge-invariant observables which, under appropriate conditions, provide good approximations to certain algebras of local fields. Our results suggest that, near any minimal hypersphere in dS, this approximation can be accurate only over regions in which the corresponding global time coordinate spans an interval of order ln G^(-1). In contrast, however, we find that the approximation can be accurate over arbitrarily large regions of global dS so long as those regions are located far to the future or past of such a minimal sphere. This talk is based on the paper arXiv:2410.00111 with Donald Marolf, Xuyang Yu, and Ying Zhao.
Quantum theories of gravity are generally expected to have some degree of nonlocality, with familiar local physics emerging only in a particular limit. Perturbative quantum gravity around backgrounds with isometries and compact Cauchy slices provides an interesting laboratory in which this emergence can be explored. In this context, the remaining isometries are gauge symmetries and, as a result, gauge-invariant observables cannot be localized. Instead, local physics can arise only through certain relational constructions. In this talk, we explore such issues for perturbative quantum gravity around de Sitter space. In particular, we describe a class of gauge-invariant observables which, under appropriate conditions, provide good approximations to certain algebras of local fields. Our results suggest that, near any minimal hypersphere in dS, this approximation can be accurate only over regions in which the corresponding global time coordinate spans an interval of order ln G^(-1). In contrast, however, we find that the approximation can be accurate over arbitrarily large regions of global dS so long as those regions are located far to the future or past of such a minimal sphere. This talk is based on the paper arXiv:2410.00111 with Donald Marolf, Xuyang Yu, and Ying Zhao.
Posted by: QMUL2
Mon
14 Apr 2025
Lonti: Lonti: Symmetries in quantum systems (4/4)
Po-Shen Hsin
(King's College London)
Abstract:
Symmetry plays an important role in quantum systems: it can constrain the dynamics, give rise to selection rules, and provide computation methods in quantum computers. In recent years there are also new types of symmetries called generalized symmetries discovered in many quantum systems, including non-invertible symmetry and higher group symmetry. These lectures will be about symmetries in various quantum systems and their applications such as constraints on the low energy dynamics. Examples will be discussed in the lectures include quantum mechanics systems, gauge theories, lattice models, and the symmetry includes ordinary and higher form symmetry as well non-invertible symmetry.
Symmetry plays an important role in quantum systems: it can constrain the dynamics, give rise to selection rules, and provide computation methods in quantum computers. In recent years there are also new types of symmetries called generalized symmetries discovered in many quantum systems, including non-invertible symmetry and higher group symmetry. These lectures will be about symmetries in various quantum systems and their applications such as constraints on the low energy dynamics. Examples will be discussed in the lectures include quantum mechanics systems, gauge theories, lattice models, and the symmetry includes ordinary and higher form symmetry as well non-invertible symmetry.
Posted by: andrea
Thu
10 Apr 2025
Emptiness Instanton in Quantum Polytropic Gas
Dimitri Gangardt
(University of Birmingham)
Abstract:
Rare macroscopic fluctuations leading to large deviations in many-body systems have attracted significant
attention in recent years. In this talk we present an exact solution to such a problem - the emptiness formation
in one-dimensional quantum polytropic gases characterized by an arbitrary polytropic index \gamma,
which defines the equation of state P ~ \rho^\gamma, where P is the pressure and \rho is the density.
The problem consists of determining the probability of spontaneous
formation of an empty interval in the ground state of the gas.
In the limit of a macroscopically large interval, this probability
is dominated by an instanton configuration. By solving the hydrodynamic equations in
imaginary time, we derive the analytic form of the emptiness instanton. This solution
is expressed as an integral representation analogous to those used for correlation functions
in Conformal Field Theory. Prominent features of the spatiotemporal profile of the
instanton are obtained directly from this representation and will be discussed in the context of
limit shape phenomena.
[1] A.G. Abanov and D.M. Gangardt, arXiv:2412.1168
Rare macroscopic fluctuations leading to large deviations in many-body systems have attracted significant
attention in recent years. In this talk we present an exact solution to such a problem - the emptiness formation
in one-dimensional quantum polytropic gases characterized by an arbitrary polytropic index \gamma,
which defines the equation of state P ~ \rho^\gamma, where P is the pressure and \rho is the density.
The problem consists of determining the probability of spontaneous
formation of an empty interval in the ground state of the gas.
In the limit of a macroscopically large interval, this probability
is dominated by an instanton configuration. By solving the hydrodynamic equations in
imaginary time, we derive the analytic form of the emptiness instanton. This solution
is expressed as an integral representation analogous to those used for correlation functions
in Conformal Field Theory. Prominent features of the spatiotemporal profile of the
instanton are obtained directly from this representation and will be discussed in the context of
limit shape phenomena.
[1] A.G. Abanov and D.M. Gangardt, arXiv:2412.1168
Posted by: oxford
Thu
10 Apr 2025
Amplitudes for Hawking Radiation
📍 London
Matteo Sergola
(CEA Saclay)
Abstract:
We obtain the Hawking spectrum by exponentiating a series of Feynman diagrams describing a scalar field scattering through a collapse background. Our approach is rooted in semiclassical methods of scattering amplitudes which have recently been developed for application to gravitational-wave physics. The diagrams we encounter do not compute a standard amplitude, but rather an in-in generalisation of an amplitude which is closely connected to the Bogoliubov coefficients. We also compute the subdominant one-loop correction in our perturbative approach, analogous to the triangle correction to Schwarzschild scattering. This term can be interpreted as a finite-size correction sensitive to the radius of the black hole.
We obtain the Hawking spectrum by exponentiating a series of Feynman diagrams describing a scalar field scattering through a collapse background. Our approach is rooted in semiclassical methods of scattering amplitudes which have recently been developed for application to gravitational-wave physics. The diagrams we encounter do not compute a standard amplitude, but rather an in-in generalisation of an amplitude which is closely connected to the Bogoliubov coefficients. We also compute the subdominant one-loop correction in our perturbative approach, analogous to the triangle correction to Schwarzschild scattering. This term can be interpreted as a finite-size correction sensitive to the radius of the black hole.
Posted by: QMW
Thu
10 Apr 2025
Dark Matter as Topological Order
📍 London
Juven Wang
(LIMS, Royal Institution)
Abstract:
Th-Cosmo-talk on April 10, 2025, at KCL room K3.11.
Title: Dark Matter as Topological Order.
Abstract: We propose that topological order can replace sterile neutrinos as dark matter candidates to cancel the Standard Model global gravitational anomalies. Standard Model (SM) with 15 Weyl fermions per family (lacking the 16th, the sterile right-handed neutrino nuR) suffers from mixed gauge-gravitational anomalies tied to baryon number plus or minus lepton number B+(-)L symmetry. Including nuR per family can cancel these anomalies, but when B+(-)L symmetry is preserved as discrete finite subgroups rather than a continuous U(1), the perturbative local anomalies become nonperturbative global anomalies. We systematically enumerate these gauge-gravitational global anomalies involving discrete B+(-)L that are enhanced from the fermion parity Z2F to Z2NF. The discreteness of B+(-)L is constrained by multi-fermion deformations beyond-the-SM and the family number Nf. Unlike the free quadratic nuR Majorana mass gap preserving the minimal Z2F, we explore novel scenarios canceling (B+(-)L)-gravitational anomalies while preserving the Z2NF discrete symmetries, featuring 4-dimensional interacting gapped topological orders or gapless sectors (e.g., conformal field theories). We propose symmetric anomalous sectors as quantum dark matter to cancel SM global anomalies. We find the uniqueness of the family number at Nf = 3, such that when the representation of Z2NF from the faithful B+L for baryons at both Nf and N equal to 3 is extended to the faithful Q + NcL for quarks at N = NcNf = 9, this symmetry extension ZNc=3 to ZNcNf =9 to ZNf =3 matches with the topological order dark matter construction. Key implications include: (1) a 5th force mediating between SM and dark matter via discrete B+(-)L gauge fields, (2) dark matter as topological order quantum matter with gapped anyon excitations at ends of extended defects, and (3) Ultra Unification and topological leptogenesis. [Based on arXiv:2502.21319, arXiv:2501.00607, arXiv:2412.21196, arXiv:2411.05786, arXiv:2012.15860, arXiv:2112.14765, arXiv:2204.08393, arXiv:2302.14862, arXiv:2312.14928].
Th-Cosmo-talk on April 10, 2025, at KCL room K3.11.
Title: Dark Matter as Topological Order.
Abstract: We propose that topological order can replace sterile neutrinos as dark matter candidates to cancel the Standard Model global gravitational anomalies. Standard Model (SM) with 15 Weyl fermions per family (lacking the 16th, the sterile right-handed neutrino nuR) suffers from mixed gauge-gravitational anomalies tied to baryon number plus or minus lepton number B+(-)L symmetry. Including nuR per family can cancel these anomalies, but when B+(-)L symmetry is preserved as discrete finite subgroups rather than a continuous U(1), the perturbative local anomalies become nonperturbative global anomalies. We systematically enumerate these gauge-gravitational global anomalies involving discrete B+(-)L that are enhanced from the fermion parity Z2F to Z2NF. The discreteness of B+(-)L is constrained by multi-fermion deformations beyond-the-SM and the family number Nf. Unlike the free quadratic nuR Majorana mass gap preserving the minimal Z2F, we explore novel scenarios canceling (B+(-)L)-gravitational anomalies while preserving the Z2NF discrete symmetries, featuring 4-dimensional interacting gapped topological orders or gapless sectors (e.g., conformal field theories). We propose symmetric anomalous sectors as quantum dark matter to cancel SM global anomalies. We find the uniqueness of the family number at Nf = 3, such that when the representation of Z2NF from the faithful B+L for baryons at both Nf and N equal to 3 is extended to the faithful Q + NcL for quarks at N = NcNf = 9, this symmetry extension ZNc=3 to ZNcNf =9 to ZNf =3 matches with the topological order dark matter construction. Key implications include: (1) a 5th force mediating between SM and dark matter via discrete B+(-)L gauge fields, (2) dark matter as topological order quantum matter with gapped anyon excitations at ends of extended defects, and (3) Ultra Unification and topological leptogenesis. [Based on arXiv:2502.21319, arXiv:2501.00607, arXiv:2412.21196, arXiv:2411.05786, arXiv:2012.15860, arXiv:2112.14765, arXiv:2204.08393, arXiv:2302.14862, arXiv:2312.14928].
Posted by: oxford
Wed
9 Apr 2025
Corner charges on timelike boundaries
📍 London
Gloria Odak
(Charles U. Prague)
Abstract:
In this talk, I will revisit results on the construction of Hamiltonian surface charges in general relativity in the presence of a finite timelike boundary, with an emphasis on how different boundary conditions influence the definition of conserved quantities. The analysis, originally published a few years ago [2109.02883], focuses on Dirichlet, Neumann, and York's mixed boundary conditions, and demonstrates how each leads to consistent, integrable charges using canonical methods. These results are shown to match those obtained via a covariant phase space formalism enhanced by a boundary Lagrangian. A key outcome of the study is the identification of an integrable charge for the Einstein-Hilbert action that differs from Komar's and remains well-defined even without Killing symmetries. We also analyze how the charge depends on the choice of boundary conditions, demonstrating that both quasi-local and asymptotic expressions are affected. These findings are relevant to current efforts to understand gravitational dynamics in finite regions and may have implications for the thermodynamics of black holes.
In this talk, I will revisit results on the construction of Hamiltonian surface charges in general relativity in the presence of a finite timelike boundary, with an emphasis on how different boundary conditions influence the definition of conserved quantities. The analysis, originally published a few years ago [2109.02883], focuses on Dirichlet, Neumann, and York's mixed boundary conditions, and demonstrates how each leads to consistent, integrable charges using canonical methods. These results are shown to match those obtained via a covariant phase space formalism enhanced by a boundary Lagrangian. A key outcome of the study is the identification of an integrable charge for the Einstein-Hilbert action that differs from Komar's and remains well-defined even without Killing symmetries. We also analyze how the charge depends on the choice of boundary conditions, demonstrating that both quasi-local and asymptotic expressions are affected. These findings are relevant to current efforts to understand gravitational dynamics in finite regions and may have implications for the thermodynamics of black holes.
Posted by: andrea
Mon
7 Apr 2025
Lonti: Symmetries in quantum systems (3/4)
Po-Shen Hsin
(King's College London)
Abstract:
Symmetry plays an important role in quantum systems: it can constrain the dynamics, give rise to selection rules, and provide computation methods in quantum computers. In recent years there are also new types of symmetries called generalized symmetries discovered in many quantum systems, including non-invertible symmetry and higher group symmetry. These lectures will be about symmetries in various quantum systems and their applications such as constraints on the low energy dynamics. Examples will be discussed in the lectures include quantum mechanics systems, gauge theories, lattice models, and the symmetry includes ordinary and higher form symmetry as well non-invertible symmetry.
Symmetry plays an important role in quantum systems: it can constrain the dynamics, give rise to selection rules, and provide computation methods in quantum computers. In recent years there are also new types of symmetries called generalized symmetries discovered in many quantum systems, including non-invertible symmetry and higher group symmetry. These lectures will be about symmetries in various quantum systems and their applications such as constraints on the low energy dynamics. Examples will be discussed in the lectures include quantum mechanics systems, gauge theories, lattice models, and the symmetry includes ordinary and higher form symmetry as well non-invertible symmetry.
Posted by: andrea
Thu
3 Apr 2025
Integrable deformations of AdS3 strings
📍 London
Fiona Seibold
(University of Hamburg)
Abstract:
Free strings on backgrounds such as AdS3xS3xT4 and AdS3xS3xS3xS1 can be described by integrable sigma models, which admit a very rich landscape of integrable deformations. In this talk I will focus on TsT, trigonometric and elliptic deformations which preserve some amount of supersymmetries and interpolate between well-known integrable setups. I will present the deformed geometry and check that the S-matrix encoding the scattering of excitations on the string worldsheet is compatible with factorisation.
Free strings on backgrounds such as AdS3xS3xT4 and AdS3xS3xS3xS1 can be described by integrable sigma models, which admit a very rich landscape of integrable deformations. In this talk I will focus on TsT, trigonometric and elliptic deformations which preserve some amount of supersymmetries and interpolate between well-known integrable setups. I will present the deformed geometry and check that the S-matrix encoding the scattering of excitations on the string worldsheet is compatible with factorisation.
Posted by: QMW
Wed
2 Apr 2025
Towards a Flat-Space Carrollian Hologram from AdS/CFT
📍 London
Romain Ruzziconi
(Oxford U.)
Abstract:
Carrollian holography suggests that gravity in four-dimensional (4d) asymptotically flat spacetime is dual to a three-dimensional (3d) Carrollian CFT living at null infinity. In this talk, I will review this framework and explain how massless scattering amplitudes in flat space can be recast as Carrollian CFT correlators at null infinity, referred to as Carrollian amplitudes. I will show that these correlators arise naturally from the Carrollian limit of holographic CFT correlators computed via AdS Witten diagrams, establishing a correspondence between the flat-space limit in the bulk and the Carrollian limit at the boundary. As a concrete application, I will briefly discuss the flat-space/Carrollian limit of the duality between 11d supergravity on AdS_4xS^7 and the 3d ABJM theory.
Based on arXiv:2312.10138, arXiv:2406.19343 and work in progress.
Carrollian holography suggests that gravity in four-dimensional (4d) asymptotically flat spacetime is dual to a three-dimensional (3d) Carrollian CFT living at null infinity. In this talk, I will review this framework and explain how massless scattering amplitudes in flat space can be recast as Carrollian CFT correlators at null infinity, referred to as Carrollian amplitudes. I will show that these correlators arise naturally from the Carrollian limit of holographic CFT correlators computed via AdS Witten diagrams, establishing a correspondence between the flat-space limit in the bulk and the Carrollian limit at the boundary. As a concrete application, I will briefly discuss the flat-space/Carrollian limit of the duality between 11d supergravity on AdS_4xS^7 and the 3d ABJM theory.
Based on arXiv:2312.10138, arXiv:2406.19343 and work in progress.
Posted by: andrea
March 2025
Mon
31 Mar 2025
Lonti: Lonti: Symmetries in quantum systems (2/4)
Po-Shen Hsin
(King's College London)
Abstract:
Symmetry plays an important role in quantum systems: it can constrain the dynamics, give rise to selection rules, and provide computation methods in quantum computers. In recent years there are also new types of symmetries called generalized symmetries discovered in many quantum systems, including non-invertible symmetry and higher group symmetry. These lectures will be about symmetries in various quantum systems and their applications such as constraints on the low energy dynamics. Examples will be discussed in the lectures include quantum mechanics systems, gauge theories, lattice models, and the symmetry includes ordinary and higher form symmetry as well non-invertible symmetry.
Symmetry plays an important role in quantum systems: it can constrain the dynamics, give rise to selection rules, and provide computation methods in quantum computers. In recent years there are also new types of symmetries called generalized symmetries discovered in many quantum systems, including non-invertible symmetry and higher group symmetry. These lectures will be about symmetries in various quantum systems and their applications such as constraints on the low energy dynamics. Examples will be discussed in the lectures include quantum mechanics systems, gauge theories, lattice models, and the symmetry includes ordinary and higher form symmetry as well non-invertible symmetry.
Posted by: andrea
Thu
27 Mar 2025
AI for QFT
Koji Hashimoto
(Kyoto university)
Abstract:
14:00-14.30
Speaker: Koji Hashimoto (Kyoto university)
Title: "Neural network representation of quantum systems"
Abstract:
We provide a novel map with which a wide class of quantum mechanical systems can be cast into the form of a neural network with a statistical summation over network parameters. Our simple idea is to use the universal approximation theorem of neural networks to generate arbitrary paths in the Feynman's path integral. The map can be applied to interacting quantum systems / field theories, even away from the Gaussian limit. Our findings bring machine learning closer to the quantum world. The talk is based on a collaboration with Y. Hirono, J. Maeda and J. Totsuka-Yoshinaka, https://arxiv.org/abs/2403.11420
14:30-15:00
Speaker: Akio Tomiya (Tokyo Woman's Christian University)
Title: "CASK: A Gauge Covariant Transformer for Lattice Gauge Theory"
Abstract:
We introduce a Transformer architecture for lattice QCD that is designed to respect the gauge symmetry and the discrete rotational and translational symmetries of the lattice. The core innovation lies in defining the attention matrix via a Frobenius inner product between link variables and extended staples, ensuring gauge covariance. We apply this method to self-learning HMC and find that it surpasses existing gauge covariant neural networks in performance, demonstrating its potential to enhance lattice QCD computations. This talk is based on arXiv:2501.16955.
14:00-14.30
Speaker: Koji Hashimoto (Kyoto university)
Title: "Neural network representation of quantum systems"
Abstract:
We provide a novel map with which a wide class of quantum mechanical systems can be cast into the form of a neural network with a statistical summation over network parameters. Our simple idea is to use the universal approximation theorem of neural networks to generate arbitrary paths in the Feynman's path integral. The map can be applied to interacting quantum systems / field theories, even away from the Gaussian limit. Our findings bring machine learning closer to the quantum world. The talk is based on a collaboration with Y. Hirono, J. Maeda and J. Totsuka-Yoshinaka, https://arxiv.org/abs/2403.11420
14:30-15:00
Speaker: Akio Tomiya (Tokyo Woman's Christian University)
Title: "CASK: A Gauge Covariant Transformer for Lattice Gauge Theory"
Abstract:
We introduce a Transformer architecture for lattice QCD that is designed to respect the gauge symmetry and the discrete rotational and translational symmetries of the lattice. The core innovation lies in defining the attention matrix via a Frobenius inner product between link variables and extended staples, ensuring gauge covariance. We apply this method to self-learning HMC and find that it surpasses existing gauge covariant neural networks in performance, demonstrating its potential to enhance lattice QCD computations. This talk is based on arXiv:2501.16955.
Posted by: oxford
Thu
27 Mar 2025
On the deep string spectrum
📍 London
Chrysoula Markou
(Scuola Normale Superiore di Pisa)
Abstract:
How well do we understand string theory? As one indicator can be thought of the degree of our understanding of its spectrum. Yet, other than comprising infinitely many physical states of arbitrarily high spin and mass, what does the string spectrum look like? Traditional methodologies can yield its state content on a level-by-level basis, a straightforward procedure which however becomes cumbersome as the level increases. In this seminar, we will discuss a new, covariant and efficient technology with which entire physical trajectories can be excavated. It is based on the observation that the Virasoro constraints in fact encode the generators of a bigger algebra, that is a symplectic algebra, which commutes with the spacetime Lorentz algebra. This enables constructing trajectories deeper inside the spectrum as clones of simpler ones, upon suitably dressing the latter, depending on the depth of the trajectory we aim to reach.
How well do we understand string theory? As one indicator can be thought of the degree of our understanding of its spectrum. Yet, other than comprising infinitely many physical states of arbitrarily high spin and mass, what does the string spectrum look like? Traditional methodologies can yield its state content on a level-by-level basis, a straightforward procedure which however becomes cumbersome as the level increases. In this seminar, we will discuss a new, covariant and efficient technology with which entire physical trajectories can be excavated. It is based on the observation that the Virasoro constraints in fact encode the generators of a bigger algebra, that is a symplectic algebra, which commutes with the spacetime Lorentz algebra. This enables constructing trajectories deeper inside the spectrum as clones of simpler ones, upon suitably dressing the latter, depending on the depth of the trajectory we aim to reach.
Posted by: QMW
Thu
27 Mar 2025
Hidden Symmetries in N=2 Superconformal Theories
Konstantinos Zoubos
(University of Pretoria)
Abstract:
Orbifolding the N=4 SYM theory naively breaks its SU(4) R-symmetry group to a much smaller subgroup, such as SU(2)xU(1) if N=2 supersymmetry is preserved. I will discuss how, by extending our notion of symmetry to include Lie groupoids and their twists, one can recover the broken generators and show that, at the planar level, a version of the full SU(4) symmetry is still present. I will briefly discuss the implications of this hidden symmetry as far as the planar spectrum of the theory is concerned.
Orbifolding the N=4 SYM theory naively breaks its SU(4) R-symmetry group to a much smaller subgroup, such as SU(2)xU(1) if N=2 supersymmetry is preserved. I will discuss how, by extending our notion of symmetry to include Lie groupoids and their twists, one can recover the broken generators and show that, at the planar level, a version of the full SU(4) symmetry is still present. I will briefly discuss the implications of this hidden symmetry as far as the planar spectrum of the theory is concerned.
Posted by: oxford
Wed
26 Mar 2025
Localisation of the M2-brane
📍 London
Fridrik Gautason
(Southampton University)
Abstract:
I will discuss the M2-brane partition function for large class of asymptotically locally AdS_4 x S^7 spacetimes. I will show how supersymmetry localises the M2-brane position to a fixed point of an R-symmetry Killing vector. I will then discuss the one-loop partition function of instantonic M2-branes and show that it is assembled out of building blocks familiar to 3D supersymmetric quantum field theories. I will close out with a discussion of possible one-loop exactness of the answer and what it means for supersymmetric localisation of the M2-brane partition function.
I will discuss the M2-brane partition function for large class of asymptotically locally AdS_4 x S^7 spacetimes. I will show how supersymmetry localises the M2-brane position to a fixed point of an R-symmetry Killing vector. I will then discuss the one-loop partition function of instantonic M2-branes and show that it is assembled out of building blocks familiar to 3D supersymmetric quantum field theories. I will close out with a discussion of possible one-loop exactness of the answer and what it means for supersymmetric localisation of the M2-brane partition function.
Posted by: andrea
Mon
24 Mar 2025
Lonti: Symmetries in quantum systems (1/4)
Po-Shen Hsin
(King's College London)
Abstract:
Symmetry plays an important role in quantum systems: it can constrain the dynamics, give rise to selection rules, and provide computation methods in quantum computers. In recent years there are also new types of symmetries called generalized symmetries discovered in many quantum systems, including non-invertible symmetry and higher group symmetry. These lectures will be about symmetries in various quantum systems and their applications such as constraints on the low energy dynamics. Examples will be discussed in the lectures include quantum mechanics systems, gauge theories, lattice models, and the symmetry includes ordinary and higher form symmetry as well non-invertible symmetry.
Symmetry plays an important role in quantum systems: it can constrain the dynamics, give rise to selection rules, and provide computation methods in quantum computers. In recent years there are also new types of symmetries called generalized symmetries discovered in many quantum systems, including non-invertible symmetry and higher group symmetry. These lectures will be about symmetries in various quantum systems and their applications such as constraints on the low energy dynamics. Examples will be discussed in the lectures include quantum mechanics systems, gauge theories, lattice models, and the symmetry includes ordinary and higher form symmetry as well non-invertible symmetry.
Posted by: andrea
Wed
19 Mar 2025
TBA
Kamran Vaziri
(Amsterdam U.)
Wed
19 Mar 2025
QFTs on AdS
📍 London
Elias Kiritsis
(Crete U.)
Abstract:
I will provide a rather lengthy introduction in oder to highlight interest in exploring QFts on AdS spaces (without dynamical gravity). The aspects involve the dyanmics of boundaries and interfaces in normal QFTs in flat space, the actual dynamics of confining gauge theories on AdS, the question of prximity in the pace of QFRTs, a more general notion of holography and its connection to S-matrices and finally Euclidean wormholes.
All these issues will connect in the effort to describe holographic QFTs on AdS.
We shall investigate in a concrete example how the related classical solutions explore the space of QFTs and we construct the general solutions that interpolate between the same or different CFTs with arbitrary couplings. The solution space contains many exotic RG flow solutions that realize unusual asymptotics, as boundaries of different regions in the space of solutions. We find phenomena like "walking" flows and the generation of extra boundaries via "flow fragmentation".
We will then move on and describe an example of a holographic theory that confines on flat space, when we put it on AdS.
We will find three types of regular solutions are found. Theories with two AdS boundaries provide interfaces between two confining theories. Theories with a single AdS boundary correspond to ground states of a single confining theory on AdS. We find solutions without a boundary, whose interpretation is
probably as interfaces between topological theories. We analyze in detail the holographic dictionary for the one-boundary solutions and compute the free energy. No (quantum) phase transitions are found when we change the curvature. We find an infinite number of pure vev solutions, but no CFT solution without a vev. We also compute the free energy of the interface solutions. We find that the product saddle points have always lower free energy than the connected solutions. Finally we will comment on the spectrum of propa gating states of holographic theories on AdS and dS.
I will provide a rather lengthy introduction in oder to highlight interest in exploring QFts on AdS spaces (without dynamical gravity). The aspects involve the dyanmics of boundaries and interfaces in normal QFTs in flat space, the actual dynamics of confining gauge theories on AdS, the question of prximity in the pace of QFRTs, a more general notion of holography and its connection to S-matrices and finally Euclidean wormholes.
All these issues will connect in the effort to describe holographic QFTs on AdS.
We shall investigate in a concrete example how the related classical solutions explore the space of QFTs and we construct the general solutions that interpolate between the same or different CFTs with arbitrary couplings. The solution space contains many exotic RG flow solutions that realize unusual asymptotics, as boundaries of different regions in the space of solutions. We find phenomena like "walking" flows and the generation of extra boundaries via "flow fragmentation".
We will then move on and describe an example of a holographic theory that confines on flat space, when we put it on AdS.
We will find three types of regular solutions are found. Theories with two AdS boundaries provide interfaces between two confining theories. Theories with a single AdS boundary correspond to ground states of a single confining theory on AdS. We find solutions without a boundary, whose interpretation is
probably as interfaces between topological theories. We analyze in detail the holographic dictionary for the one-boundary solutions and compute the free energy. No (quantum) phase transitions are found when we change the curvature. We find an infinite number of pure vev solutions, but no CFT solution without a vev. We also compute the free energy of the interface solutions. We find that the product saddle points have always lower free energy than the connected solutions. Finally we will comment on the spectrum of propa gating states of holographic theories on AdS and dS.
Posted by: andrea
Tue
18 Mar 2025
Topological Order as Dark Matter
📍 London
Juven Wang
(LIMS)
Abstract:
In this talk, we propose that topological order can replace sterile neutrinos as dark matter candidates to cancel the Standard Model global gravitational anomalies. Standard Model (SM) with 15 Weyl fermions per family (lacking the 16th, the sterile right-handed neutrino nuR) suffers from mixed gauge-gravitational anomalies tied to baryon number plus or minus lepton number B+(-)L symmetry. Including nuR per family can cancel these anomalies, but when B+(-)L symmetry is preserved as discrete finite subgroups rather than a continuous U(1), the perturbative local anomalies become nonperturbative global anomalies. We systematically enumerate these gauge-gravitational global anomalies involving discrete B+(-)L that are enhanced from the fermion parity ZF2 to ZF2N. The discreteness of B+(-)L is constrained by multi-fermion deformations beyond-the-SM and the family number Nf. Unlike the free quadratic nuR Majorana mass gap preserving the minimal ZF2, we explore novel scenarios canceling (B+(-)L)-gravitational anomalies while preserving the ZF2N discrete symmetries, featuring 4-dimensional interacting gapped topological orders or gapless sectors (e.g., conformal field theories). We propose symmetric anomalous sectors as quantum dark matter to cancel SM global anomalies. We find the uniqueness of the family number at Nf = 3, such that when the representation of ZF2N from the faithful B+L for baryons at both Nf and N equal to 3 is extended to the faithful Q + NcL for quarks at N = NcNf = 9, this symmetry extension ZNc=3 to ZNcNf =9 to ZNf =3 matches with the topological order dark matter construction. Key implications include: (1) a 5th force mediating between SM and dark matter via discrete B+(-)L gauge fields, (2) dark matter as topological order quantum matter with gapped anyon excitations at ends of extended defects, and (3) Ultra Unification and topological leptogenesis. [Based on arXiv:2502.21319, arXiv:2501.00607, arXiv:2411.05786, arXiv:2012.15860, arXiv:2112.14765, arXiv:2204.08393, arXiv:2302.14862, arXiv:2312.14928].
In this talk, we propose that topological order can replace sterile neutrinos as dark matter candidates to cancel the Standard Model global gravitational anomalies. Standard Model (SM) with 15 Weyl fermions per family (lacking the 16th, the sterile right-handed neutrino nuR) suffers from mixed gauge-gravitational anomalies tied to baryon number plus or minus lepton number B+(-)L symmetry. Including nuR per family can cancel these anomalies, but when B+(-)L symmetry is preserved as discrete finite subgroups rather than a continuous U(1), the perturbative local anomalies become nonperturbative global anomalies. We systematically enumerate these gauge-gravitational global anomalies involving discrete B+(-)L that are enhanced from the fermion parity ZF2 to ZF2N. The discreteness of B+(-)L is constrained by multi-fermion deformations beyond-the-SM and the family number Nf. Unlike the free quadratic nuR Majorana mass gap preserving the minimal ZF2, we explore novel scenarios canceling (B+(-)L)-gravitational anomalies while preserving the ZF2N discrete symmetries, featuring 4-dimensional interacting gapped topological orders or gapless sectors (e.g., conformal field theories). We propose symmetric anomalous sectors as quantum dark matter to cancel SM global anomalies. We find the uniqueness of the family number at Nf = 3, such that when the representation of ZF2N from the faithful B+L for baryons at both Nf and N equal to 3 is extended to the faithful Q + NcL for quarks at N = NcNf = 9, this symmetry extension ZNc=3 to ZNcNf =9 to ZNf =3 matches with the topological order dark matter construction. Key implications include: (1) a 5th force mediating between SM and dark matter via discrete B+(-)L gauge fields, (2) dark matter as topological order quantum matter with gapped anyon excitations at ends of extended defects, and (3) Ultra Unification and topological leptogenesis. [Based on arXiv:2502.21319, arXiv:2501.00607, arXiv:2411.05786, arXiv:2012.15860, arXiv:2112.14765, arXiv:2204.08393, arXiv:2302.14862, arXiv:2312.14928].
Posted by: QMW
Mon
17 Mar 2025
Lonti: Exploring the IR and UV Regimes of QCD (4/4)
Andrea Guerrieri
(City U.)
Abstract:
Quantum Chromodynamics (QCD) has been a profound source of inspiration for theoretical physics, driving the development of key concepts such as string theory, effective field theories, instantons, anomalies, and lattice gauge theories. In these lectures, I will explore two distinct regimes of QCD - its infrared (IR) and ultraviolet (UV) limits - and the theoretical tools used to study them.
In the IR regime, where perturbative techniques break down, Effective Field Theories (EFTs) provide a powerful framework. I will introduce the pion EFT as a tool to study non-linearly realized symmetries and soft theorems. In the UV regime, where QCD becomes amenable to perturbative analysis, I will discuss the Operator Product Expansion and renormalization group equations, focusing on their application to deep inelastic scattering, a cornerstone in the discovery of quarks and gluons.
These two regimes illustrate the richness of QCD and its pivotal role in shaping our understanding of fundamental physics.
Quantum Chromodynamics (QCD) has been a profound source of inspiration for theoretical physics, driving the development of key concepts such as string theory, effective field theories, instantons, anomalies, and lattice gauge theories. In these lectures, I will explore two distinct regimes of QCD - its infrared (IR) and ultraviolet (UV) limits - and the theoretical tools used to study them.
In the IR regime, where perturbative techniques break down, Effective Field Theories (EFTs) provide a powerful framework. I will introduce the pion EFT as a tool to study non-linearly realized symmetries and soft theorems. In the UV regime, where QCD becomes amenable to perturbative analysis, I will discuss the Operator Product Expansion and renormalization group equations, focusing on their application to deep inelastic scattering, a cornerstone in the discovery of quarks and gluons.
These two regimes illustrate the richness of QCD and its pivotal role in shaping our understanding of fundamental physics.
Posted by: andrea
Thu
13 Mar 2025
(Super)blocks, free block coefficients, and applications to N=4 SYM at strong coupling
📍 London
Paul Heslop
(Durham University)
Abstract:
Recently a formula for free theory (super)block coefficients in many SCFTs was first guessed and then proved https://arxiv.org/abs/2502.14077. I will describe this result and summarise some of the background to it, involving a number of beautiful relations between superblocks, symmetric polynomials, superJacobi polynomials, Heckman Opdam hypergeometric functions, Calogero Sutherland Moser wave functions and Cauchy identities. I will also give a new application to strong coupling N=4 SYM.
Recently a formula for free theory (super)block coefficients in many SCFTs was first guessed and then proved https://arxiv.org/abs/2502.14077. I will describe this result and summarise some of the background to it, involving a number of beautiful relations between superblocks, symmetric polynomials, superJacobi polynomials, Heckman Opdam hypergeometric functions, Calogero Sutherland Moser wave functions and Cauchy identities. I will also give a new application to strong coupling N=4 SYM.
Posted by: QMW
Wed
12 Mar 2025
Yangian symmetry, GKZ equations and integrable Feynman graphs
📍 London
Fedor Levkovich-Maslyuk
(City University London)
Abstract:
We extend the powerful property of Yangian invariance to a new large class of conformally invariant multi-loop Feynman integrals. This leads to new highly constraining differential equations for them, making integrability visible at the level of individual Feynman graphs. Our results apply to planar Feynman diagrams in any spacetime dimension dual to an arbitrary network of intersecting straight lines on a plane (Baxter lattice), with propagator powers determined by the geometry. The graphs we consider determine correlators in the recently proposed "loom" fishnet CFTs. The construction unifies and greatly extends the known special cases of Yangian invariance to likely the most general family of integrable scalar planar graphs. We also relate these equations in certain cases to famous GKZ (Gelfand-Kapranov-Zelevinsky) hypergeometric operators, opening the way to using new powerful solution methods.
We extend the powerful property of Yangian invariance to a new large class of conformally invariant multi-loop Feynman integrals. This leads to new highly constraining differential equations for them, making integrability visible at the level of individual Feynman graphs. Our results apply to planar Feynman diagrams in any spacetime dimension dual to an arbitrary network of intersecting straight lines on a plane (Baxter lattice), with propagator powers determined by the geometry. The graphs we consider determine correlators in the recently proposed "loom" fishnet CFTs. The construction unifies and greatly extends the known special cases of Yangian invariance to likely the most general family of integrable scalar planar graphs. We also relate these equations in certain cases to famous GKZ (Gelfand-Kapranov-Zelevinsky) hypergeometric operators, opening the way to using new powerful solution methods.
Posted by: andrea
Thu
6 Mar 2025
Pure-spinor amplitudes without pure spinors
📍 London
Thales Azevedo
(Federal University of Rio de Janeiro)
Abstract:
Since its discovery by Berkovits 25 years ago, the pure-spinor formulation of the superstring has proven to be a very useful tool in the calculation of scattering amplitudes, both at tree- and loop-level. However, almost all of its applications are confined to the scattering of massless states. Computation of massive string amplitudes is possible in principle, but difficult to perform within the usual pure-spinor prescription. In this talk, I will report progress on computing manifestly super-Poincare invariant amplitudes through an alternative procedure, which does not explicitly involve the pure-spinor variable and should apply equally well to massless and massive external states.
Since its discovery by Berkovits 25 years ago, the pure-spinor formulation of the superstring has proven to be a very useful tool in the calculation of scattering amplitudes, both at tree- and loop-level. However, almost all of its applications are confined to the scattering of massless states. Computation of massive string amplitudes is possible in principle, but difficult to perform within the usual pure-spinor prescription. In this talk, I will report progress on computing manifestly super-Poincare invariant amplitudes through an alternative procedure, which does not explicitly involve the pure-spinor variable and should apply equally well to massless and massive external states.
Posted by: QMW
Wed
5 Mar 2025
Categorical description of fermionic topological theories in 3+1d
Matthew Yu
(Oxford)
Abstract:
Topological field theories, or what is otherwise commonly known as topological orders, can be given a rigorous axiomization in terms of higher fusion categories with some extra structure. The extra structure is necessary to incorporate the relevant physical properties of topological orders. With this categorical framework we can give classifications of topological orders in low dimensions. I will explain how this is done for (3+1)d topological orders that are fermionic in nature.
with Pedagogical Intro by Juven Wang
Topological field theories, or what is otherwise commonly known as topological orders, can be given a rigorous axiomization in terms of higher fusion categories with some extra structure. The extra structure is necessary to incorporate the relevant physical properties of topological orders. With this categorical framework we can give classifications of topological orders in low dimensions. I will explain how this is done for (3+1)d topological orders that are fermionic in nature.
with Pedagogical Intro by Juven Wang
Posted by: oxford
Wed
5 Mar 2025
Duality of Decaying Turbulence to a Solvable String Theory
Alexander Migdal
(IAS)
Abstract:
We propose a novel analytical framework for incompressible Navier-Stokes (NS) turbulence, revealing a duality between classical fluid dynamics and one-dimensional nonlinear dynamics in loop space.
This reformulation leads to a universal momentum loop equation, which excludes finite-time blow-ups, establishing a No Explosion Theorem for turbulent flows with finite initial noise.
Decaying turbulence emerges as a solution to this equation and is interpreted as a solvable string theory with a discrete target space composed of regular star polygons.
The derived decay spectrum exhibits excellent agreement with experimental data and direct numerical simulations (DNS), replacing classical Kolmogorov scaling laws with universal functions derived from number theory.
These results suggest a deeper mathematical structure underlying turbulence, uniting fluid dynamics, quantum mechanics, and number theory.
We propose a novel analytical framework for incompressible Navier-Stokes (NS) turbulence, revealing a duality between classical fluid dynamics and one-dimensional nonlinear dynamics in loop space.
This reformulation leads to a universal momentum loop equation, which excludes finite-time blow-ups, establishing a No Explosion Theorem for turbulent flows with finite initial noise.
Decaying turbulence emerges as a solution to this equation and is interpreted as a solvable string theory with a discrete target space composed of regular star polygons.
The derived decay spectrum exhibits excellent agreement with experimental data and direct numerical simulations (DNS), replacing classical Kolmogorov scaling laws with universal functions derived from number theory.
These results suggest a deeper mathematical structure underlying turbulence, uniting fluid dynamics, quantum mechanics, and number theory.
Posted by: IC2
Wed
5 Mar 2025
Localization of the 5D supergravity action and saddles of the black hole index
📍 London
Davide Cassani
(Padua U.)
Abstract:
About fifty years ago, Gibbons and Hawking argued that the Euclidean gravitational path integral with suitable boundary conditions can be interpreted as a grand-canonical partition function. Classical gravitational solutions, including black holes, arise as saddles of this path integral, and from the saddle-point action one can extract the black hole entropy. In the talk, I will discuss some recent developments of these ideas. Working in five dimensions, we will see how imposing supersymmetric boundary conditions converts the partition function into an index. Then we will construct a class of saddles of this index which interpolates between supersymmetric black holes and horizonless microstate geometries. I will discuss how the saddle point action can be computed via equivariant localization. Finally, I will comment on the relevance of these findings for black hole microstate counting and holography.
About fifty years ago, Gibbons and Hawking argued that the Euclidean gravitational path integral with suitable boundary conditions can be interpreted as a grand-canonical partition function. Classical gravitational solutions, including black holes, arise as saddles of this path integral, and from the saddle-point action one can extract the black hole entropy. In the talk, I will discuss some recent developments of these ideas. Working in five dimensions, we will see how imposing supersymmetric boundary conditions converts the partition function into an index. Then we will construct a class of saddles of this index which interpolates between supersymmetric black holes and horizonless microstate geometries. I will discuss how the saddle point action can be computed via equivariant localization. Finally, I will comment on the relevance of these findings for black hole microstate counting and holography.
Posted by: andrea
Mon
3 Mar 2025
Lonti: Exploring the IR and UV Regimes of QCD (3/4)
Andrea Guerrieri
(City U.)
Abstract:
Quantum Chromodynamics (QCD) has been a profound source of inspiration for theoretical physics, driving the development of key concepts such as string theory, effective field theories, instantons, anomalies, and lattice gauge theories. In these lectures, I will explore two distinct regimes of QCD - its infrared (IR) and ultraviolet (UV) limits - and the theoretical tools used to study them.
In the IR regime, where perturbative techniques break down, Effective Field Theories (EFTs) provide a powerful framework. I will introduce the pion EFT as a tool to study non-linearly realized symmetries and soft theorems. In the UV regime, where QCD becomes amenable to perturbative analysis, I will discuss the Operator Product Expansion and renormalization group equations, focusing on their application to deep inelastic scattering, a cornerstone in the discovery of quarks and gluons.
These two regimes illustrate the richness of QCD and its pivotal role in shaping our understanding of fundamental physics.
Quantum Chromodynamics (QCD) has been a profound source of inspiration for theoretical physics, driving the development of key concepts such as string theory, effective field theories, instantons, anomalies, and lattice gauge theories. In these lectures, I will explore two distinct regimes of QCD - its infrared (IR) and ultraviolet (UV) limits - and the theoretical tools used to study them.
In the IR regime, where perturbative techniques break down, Effective Field Theories (EFTs) provide a powerful framework. I will introduce the pion EFT as a tool to study non-linearly realized symmetries and soft theorems. In the UV regime, where QCD becomes amenable to perturbative analysis, I will discuss the Operator Product Expansion and renormalization group equations, focusing on their application to deep inelastic scattering, a cornerstone in the discovery of quarks and gluons.
These two regimes illustrate the richness of QCD and its pivotal role in shaping our understanding of fundamental physics.
Posted by: andrea
February 2025
Wed
26 Feb 2025
How to prove the last a-theorem
Marco Fazzi
(Sheffield U)
Abstract:
In this talk I will present two results of independent interest, the first being more mathematical in nature whereas the second more physical. I will first show that the hierarchy of so-called Higgs branch RG flows between the 6D (1,0) SCFTs known as 'A-type orbi-instantons' is given by the Hasse diagram of certain strata and transverse slices in the (conjectural) double affine Grassmannian of E8. Secondly, by leveraging the partial order naturally defined on this Hasse diagram I will present a proof of the a-theorem for 6D orbi-instanton Higgs branch RG flows, thereby exhausting the list of c-theorems in the even-dimensional (supersymmetric) setting.
In this talk I will present two results of independent interest, the first being more mathematical in nature whereas the second more physical. I will first show that the hierarchy of so-called Higgs branch RG flows between the 6D (1,0) SCFTs known as 'A-type orbi-instantons' is given by the Hasse diagram of certain strata and transverse slices in the (conjectural) double affine Grassmannian of E8. Secondly, by leveraging the partial order naturally defined on this Hasse diagram I will present a proof of the a-theorem for 6D orbi-instanton Higgs branch RG flows, thereby exhausting the list of c-theorems in the even-dimensional (supersymmetric) setting.
Posted by: IC2
Wed
26 Feb 2025
A BPS Road to Holography: Decoupling Limits and Non-Lorentzian Geometries
📍 London
Niels Obers
(NBI)
Abstract:
I explore decoupling limits that lead to matrix theories on D-branes, focusing on their BPS nature and the emergence of non-Lorentzian target space geometries. In these limits, D-branes experience instantaneous gravitational forces, and when applied to curved geometries, it is shown that a single decoupling limit leads to the AdS/CFT correspondence. By applying two such limits, we generate new holographic examples, including those with non-Lorentzian bulk geometries. I also discuss the relationship between matrix theories and non-relativistic string theory, and their uplift to M-theory. Finally, we demonstrate that reversing these decoupling limits connects to the TTbar deformation in two dimensions. This provides a new perspective on the near-horizon brane geometry and leads to TTbar-like flow equations for the Dp-brane DBI action.
I explore decoupling limits that lead to matrix theories on D-branes, focusing on their BPS nature and the emergence of non-Lorentzian target space geometries. In these limits, D-branes experience instantaneous gravitational forces, and when applied to curved geometries, it is shown that a single decoupling limit leads to the AdS/CFT correspondence. By applying two such limits, we generate new holographic examples, including those with non-Lorentzian bulk geometries. I also discuss the relationship between matrix theories and non-relativistic string theory, and their uplift to M-theory. Finally, we demonstrate that reversing these decoupling limits connects to the TTbar deformation in two dimensions. This provides a new perspective on the near-horizon brane geometry and leads to TTbar-like flow equations for the Dp-brane DBI action.
Posted by: andrea
Mon
24 Feb 2025
Lonti: Exploring the IR and UV Regimes of QCD (2/4)
Andrea Guerrieri
(City U.)
Abstract:
Quantum Chromodynamics (QCD) has been a profound source of inspiration for theoretical physics, driving the development of key concepts such as string theory, effective field theories, instantons, anomalies, and lattice gauge theories. In these lectures, I will explore two distinct regimes of QCD - its infrared (IR) and ultraviolet (UV) limits - and the theoretical tools used to study them.
In the IR regime, where perturbative techniques break down, Effective Field Theories (EFTs) provide a powerful framework. I will introduce the pion EFT as a tool to study non-linearly realized symmetries and soft theorems. In the UV regime, where QCD becomes amenable to perturbative analysis, I will discuss the Operator Product Expansion and renormalization group equations, focusing on their application to deep inelastic scattering, a cornerstone in the discovery of quarks and gluons.
These two regimes illustrate the richness of QCD and its pivotal role in shaping our understanding of fundamental physics.
Quantum Chromodynamics (QCD) has been a profound source of inspiration for theoretical physics, driving the development of key concepts such as string theory, effective field theories, instantons, anomalies, and lattice gauge theories. In these lectures, I will explore two distinct regimes of QCD - its infrared (IR) and ultraviolet (UV) limits - and the theoretical tools used to study them.
In the IR regime, where perturbative techniques break down, Effective Field Theories (EFTs) provide a powerful framework. I will introduce the pion EFT as a tool to study non-linearly realized symmetries and soft theorems. In the UV regime, where QCD becomes amenable to perturbative analysis, I will discuss the Operator Product Expansion and renormalization group equations, focusing on their application to deep inelastic scattering, a cornerstone in the discovery of quarks and gluons.
These two regimes illustrate the richness of QCD and its pivotal role in shaping our understanding of fundamental physics.
Posted by: andrea
Mon
24 Feb 2025
Universal Constraints for Conformal Line Defects
📍 London
Deliang Zhong
(Imperial College London)
Abstract:
We present a novel framework for deriving integral constraints for correlators on conformal line defects. These constraints emerge from the non-linearly realized ambient-space conformal symmetry. To validate our approach, we examine several examples and compare them against existing data for the four-point function of the displacement operator. Additionally, we provide a few new predictions that extend the current understanding of these correlators.
We present a novel framework for deriving integral constraints for correlators on conformal line defects. These constraints emerge from the non-linearly realized ambient-space conformal symmetry. To validate our approach, we examine several examples and compare them against existing data for the four-point function of the displacement operator. Additionally, we provide a few new predictions that extend the current understanding of these correlators.
Posted by: QMW
Wed
19 Feb 2025
Stringy Gregory-Laflamme
Marija Tomasevic
(Amsterdam U)
Abstract:
Thin enough black strings are unstable to growing ripples along their length, eventually pinching and forming a naked singularity on the horizon. We investigate how string theory can resolve this singularity. First, we study the string-scale version of the static non-uniform black strings that branch off at the instability threshold: "string-ball strings", which are linearly extended, self-gravitating configurations of string balls obtained in the Horowitz-Polchinski (HP) approach to near-Hagedorn string states. We construct non-uniform HP strings in spatial dimensions d≤6 and show that, as the inhomogeneity increases, they approach localized HP balls. We also examine the thermodynamic properties of the different phases in the canonical and microcanonical ensembles. We find that, for a sufficiently small mass, the uniform HP string will be stable and not evolve into a non-uniform or localized configuration. Building on these results and independent evidence from the evolution of the black string instability with α' corrections, we propose that, at least in d=4,5, string theory slows and eventually halts the pinching evolution at a classically stable stringy neck. In d≥6 this transition is likely to occur into a puffed-up string ball. The system then enters a slower phase in which the neck gradually evaporates into radiation. We discuss this scenario as a framework for understanding how string theory resolves the formation of naked singularities.
Thin enough black strings are unstable to growing ripples along their length, eventually pinching and forming a naked singularity on the horizon. We investigate how string theory can resolve this singularity. First, we study the string-scale version of the static non-uniform black strings that branch off at the instability threshold: "string-ball strings", which are linearly extended, self-gravitating configurations of string balls obtained in the Horowitz-Polchinski (HP) approach to near-Hagedorn string states. We construct non-uniform HP strings in spatial dimensions d≤6 and show that, as the inhomogeneity increases, they approach localized HP balls. We also examine the thermodynamic properties of the different phases in the canonical and microcanonical ensembles. We find that, for a sufficiently small mass, the uniform HP string will be stable and not evolve into a non-uniform or localized configuration. Building on these results and independent evidence from the evolution of the black string instability with α' corrections, we propose that, at least in d=4,5, string theory slows and eventually halts the pinching evolution at a classically stable stringy neck. In d≥6 this transition is likely to occur into a puffed-up string ball. The system then enters a slower phase in which the neck gradually evaporates into radiation. We discuss this scenario as a framework for understanding how string theory resolves the formation of naked singularities.
Posted by: IC2
Wed
19 Feb 2025
Symmetries and their breaking in quantum gravity
📍 London
Miguel Montero
(Madrid IFT)
Abstract:
The oldest and best established Swampland constraint is perhaps the idea that there are no global symmetries in quantum gravity. Traditionally, this idea has been regarded as not strong enough to strong constraints at low energies, since the quantum gravity symmetry breaking effects could be extremely weak. I will describe recent progress in Swampland, in conjunction with developments in generalized and non-invertible symmetries, which have led to the discovery of new branes in string theory, new mechanisms to engineer small couplings in string theory, and even ruling out some effective field theories in higher dimensions.
The oldest and best established Swampland constraint is perhaps the idea that there are no global symmetries in quantum gravity. Traditionally, this idea has been regarded as not strong enough to strong constraints at low energies, since the quantum gravity symmetry breaking effects could be extremely weak. I will describe recent progress in Swampland, in conjunction with developments in generalized and non-invertible symmetries, which have led to the discovery of new branes in string theory, new mechanisms to engineer small couplings in string theory, and even ruling out some effective field theories in higher dimensions.
Posted by: andrea
Mon
17 Feb 2025
Lonti: Exploring the IR and UV Regimes of QCD (1/4)
Andrea Guerrieri
(City U.)
Abstract:
Quantum Chromodynamics (QCD) has been a profound source of inspiration for theoretical physics, driving the development of key concepts such as string theory, effective field theories, instantons, anomalies, and lattice gauge theories. In these lectures, I will explore two distinct regimes of QCD - its infrared (IR) and ultraviolet (UV) limits - and the theoretical tools used to study them.
In the IR regime, where perturbative techniques break down, Effective Field Theories (EFTs) provide a powerful framework. I will introduce the pion EFT as a tool to study non-linearly realized symmetries and soft theorems. In the UV regime, where QCD becomes amenable to perturbative analysis, I will discuss the Operator Product Expansion and renormalization group equations, focusing on their application to deep inelastic scattering, a cornerstone in the discovery of quarks and gluons.
These two regimes illustrate the richness of QCD and its pivotal role in shaping our understanding of fundamental physics.
Quantum Chromodynamics (QCD) has been a profound source of inspiration for theoretical physics, driving the development of key concepts such as string theory, effective field theories, instantons, anomalies, and lattice gauge theories. In these lectures, I will explore two distinct regimes of QCD - its infrared (IR) and ultraviolet (UV) limits - and the theoretical tools used to study them.
In the IR regime, where perturbative techniques break down, Effective Field Theories (EFTs) provide a powerful framework. I will introduce the pion EFT as a tool to study non-linearly realized symmetries and soft theorems. In the UV regime, where QCD becomes amenable to perturbative analysis, I will discuss the Operator Product Expansion and renormalization group equations, focusing on their application to deep inelastic scattering, a cornerstone in the discovery of quarks and gluons.
These two regimes illustrate the richness of QCD and its pivotal role in shaping our understanding of fundamental physics.
Posted by: andrea
Thu
13 Feb 2025
Classical Double Copy: Horizons, Penrose Limits, Fluids, and Asymptotics
📍 London
Cynthia Keeler
(Arizona State University)
Abstract:
I'll briefly review the classical double copy, which maps exact solutions of classical gauge theories like electromagnetism, to solutions of general relativity. We will relate several gravitational objects (including horizons, Penrose limits, and asymptotics, and duals to fluid systems) to their gauge theory analogues.
I'll briefly review the classical double copy, which maps exact solutions of classical gauge theories like electromagnetism, to solutions of general relativity. We will relate several gravitational objects (including horizons, Penrose limits, and asymptotics, and duals to fluid systems) to their gauge theory analogues.
Posted by: QMW
Wed
12 Feb 2025
Top-down non-conformal holography
Fridrik Freyr Gautason
(University of Southampton)
Abstract:
I will discuss a few examples of holographic dual pairs that arise in string theory for quantum theories that are not conformal. In particular, we will focus on Euclidean supersymmetric gauge theories on spheres and compute observables using supergravity and string theory on one side of the duality and supersymmetric localization on the other. This two-pronged approach allows us to study perturbative and non-perturbative corrections to the leading-order holographic result.
I will discuss a few examples of holographic dual pairs that arise in string theory for quantum theories that are not conformal. In particular, we will focus on Euclidean supersymmetric gauge theories on spheres and compute observables using supergravity and string theory on one side of the duality and supersymmetric localization on the other. This two-pronged approach allows us to study perturbative and non-perturbative corrections to the leading-order holographic result.
Posted by: IC2
Wed
12 Feb 2025
Top-down non-conformal holography
Fridrik Freyr Gautason
(University of Southampton)
Abstract:
I will discuss a few examples of holographic dual pairs that arise in string theory for quantum theories that are not conformal. In particular, we will focus on Euclidean supersymmetric gauge theories on spheres and compute observables using supergravity and string theory on one side of the duality and supersymmetric localization on the other. This two-pronged approach allows us to study perturbative and non-perturbative corrections to the leading-order holographic result.
I will discuss a few examples of holographic dual pairs that arise in string theory for quantum theories that are not conformal. In particular, we will focus on Euclidean supersymmetric gauge theories on spheres and compute observables using supergravity and string theory on one side of the duality and supersymmetric localization on the other. This two-pronged approach allows us to study perturbative and non-perturbative corrections to the leading-order holographic result.
Posted by: IC2
Wed
12 Feb 2025
Monopoles, duality and QED3
📍 London
Shai Chester
(Imperial College)
Mon
10 Feb 2025
Lonti: An introduction to the black hole information paradox (4/4)
Tarek Anous
(QMUL)
Abstract:
This course will give a technical introduction to the black hole information paradox (BHIP). In the first lecture, we will begin with a review of quantum path integrals, both in Lorentzian and in Euclidean signature. We will review the Euclidean path integral connection with statistical mechanics and thermodynamics while also reviewing the derivation of the first law of thermodynamics in standard equilibrium statistical mechanics. We will then introduce the laws of black hole thermodynamics, and study them in particular examples. The second lecture will be devoted to the Unruh effect. We will study free quantum field theory in Rindler space, which, locally, is the spacetime observed by a uniformly accelerated observer. We will derive that this observer measures a temperature related to the observer proper acceleration. The third lecture will be devoted to classical and quantum information theory including notions of conditional probability, mutual information, and entropy inequalities, in settings with finite numbers of degrees of freedom. We will also introduce the Page curve and its significance. Finally, in the fourth lecture we will set up a toy model of the BHIP in Anti de Sitter space (AdS). Because AdS is believed to have a dual description as a conformal quantum field theory, we will use this duality to our advantage. We end with a broad discussion synthesizing what we have learned, and what is left to understand.
This course will give a technical introduction to the black hole information paradox (BHIP). In the first lecture, we will begin with a review of quantum path integrals, both in Lorentzian and in Euclidean signature. We will review the Euclidean path integral connection with statistical mechanics and thermodynamics while also reviewing the derivation of the first law of thermodynamics in standard equilibrium statistical mechanics. We will then introduce the laws of black hole thermodynamics, and study them in particular examples. The second lecture will be devoted to the Unruh effect. We will study free quantum field theory in Rindler space, which, locally, is the spacetime observed by a uniformly accelerated observer. We will derive that this observer measures a temperature related to the observer proper acceleration. The third lecture will be devoted to classical and quantum information theory including notions of conditional probability, mutual information, and entropy inequalities, in settings with finite numbers of degrees of freedom. We will also introduce the Page curve and its significance. Finally, in the fourth lecture we will set up a toy model of the BHIP in Anti de Sitter space (AdS). Because AdS is believed to have a dual description as a conformal quantum field theory, we will use this duality to our advantage. We end with a broad discussion synthesizing what we have learned, and what is left to understand.
Posted by: andrea
Wed
5 Feb 2025
The complex Liouville string
📍 London
Beatrix Muehlmann
(IAS)
Abstract:
I will introduce a new 2d gravity/matrix integral duality. The bulk theory is a two-dimensional string theory defined by coupling two copies of Liouville CFT with central charges c = 13 \pm is on the worldsheet. We call this string theory the complex Liouville string. I will argue that the complex Liouville string admits a dual description in terms of a double-scaled two-matrix integral. The string amplitudes, which are the main observables of the complex Liouville string, can be interpreted as cosmological correlators of massive particles, integrated over the metric at future infinity of dS3 to define gauge invariant observables. Furthermore we obtain evidence that the dS3 Gibbons-Hawking entropy can be reproduced exactly by counting the degrees of freedom in the dual matrix integral.
I will introduce a new 2d gravity/matrix integral duality. The bulk theory is a two-dimensional string theory defined by coupling two copies of Liouville CFT with central charges c = 13 \pm is on the worldsheet. We call this string theory the complex Liouville string. I will argue that the complex Liouville string admits a dual description in terms of a double-scaled two-matrix integral. The string amplitudes, which are the main observables of the complex Liouville string, can be interpreted as cosmological correlators of massive particles, integrated over the metric at future infinity of dS3 to define gauge invariant observables. Furthermore we obtain evidence that the dS3 Gibbons-Hawking entropy can be reproduced exactly by counting the degrees of freedom in the dual matrix integral.
Posted by: QMW
Wed
5 Feb 2025
Fuzzy sphere regularization of 3D CFTs
📍 London
Yin-Chen He
(Stony Brook University)
Abstract:
Conformal Field Theory (CFT) represents a class of quantum field theories that have profound applications across various physics domains, from critical phenomena in statistical mechanics to quantum matter, quantum gravity, and string theory. In this talk, I will introduce our recently proposed fuzzy (non-commutative) sphere regularization scheme, a method that addresses and offers a solution to the longstanding need for a non-perturbative approach to 3D CFTs. I will first elucidate its fundamental concepts and then dive into illustrative examples, including the 3D Ising transition, conformal defects, and critical gauge theories. Importantly, I will showcase that this scheme is not only potent–revealing a wealth of universal data on 3D CFTs otherwise inaccessible through existing methods–but also efficient, as the necessary computations can be performed on a laptop within an hour. Our innovative scheme not only heralds a new era for the study of CFTs but also hints at a profound interplay between non-commutative geometry and both CFTs and QFTs at large.
Conformal Field Theory (CFT) represents a class of quantum field theories that have profound applications across various physics domains, from critical phenomena in statistical mechanics to quantum matter, quantum gravity, and string theory. In this talk, I will introduce our recently proposed fuzzy (non-commutative) sphere regularization scheme, a method that addresses and offers a solution to the longstanding need for a non-perturbative approach to 3D CFTs. I will first elucidate its fundamental concepts and then dive into illustrative examples, including the 3D Ising transition, conformal defects, and critical gauge theories. Importantly, I will showcase that this scheme is not only potent–revealing a wealth of universal data on 3D CFTs otherwise inaccessible through existing methods–but also efficient, as the necessary computations can be performed on a laptop within an hour. Our innovative scheme not only heralds a new era for the study of CFTs but also hints at a profound interplay between non-commutative geometry and both CFTs and QFTs at large.
Posted by: QMW
Mon
3 Feb 2025
Lonti: An introduction to the black hole information paradox (3/4)
Tarek Anous
(QMUL)
Abstract:
This course will give a technical introduction to the black hole information paradox (BHIP). In the first lecture, we will begin with a review of quantum path integrals, both in Lorentzian and in Euclidean signature. We will review the Euclidean path integral connection with statistical mechanics and thermodynamics while also reviewing the derivation of the first law of thermodynamics in standard equilibrium statistical mechanics. We will then introduce the laws of black hole thermodynamics, and study them in particular examples. The second lecture will be devoted to the Unruh effect. We will study free quantum field theory in Rindler space, which, locally, is the spacetime observed by a uniformly accelerated observer. We will derive that this observer measures a temperature related to the observer proper acceleration. The third lecture will be devoted to classical and quantum information theory including notions of conditional probability, mutual information, and entropy inequalities, in settings with finite numbers of degrees of freedom. We will also introduce the Page curve and its significance. Finally, in the fourth lecture we will set up a toy model of the BHIP in Anti de Sitter space (AdS). Because AdS is believed to have a dual description as a conformal quantum field theory, we will use this duality to our advantage. We end with a broad discussion synthesizing what we have learned, and what is left to understand.
This course will give a technical introduction to the black hole information paradox (BHIP). In the first lecture, we will begin with a review of quantum path integrals, both in Lorentzian and in Euclidean signature. We will review the Euclidean path integral connection with statistical mechanics and thermodynamics while also reviewing the derivation of the first law of thermodynamics in standard equilibrium statistical mechanics. We will then introduce the laws of black hole thermodynamics, and study them in particular examples. The second lecture will be devoted to the Unruh effect. We will study free quantum field theory in Rindler space, which, locally, is the spacetime observed by a uniformly accelerated observer. We will derive that this observer measures a temperature related to the observer proper acceleration. The third lecture will be devoted to classical and quantum information theory including notions of conditional probability, mutual information, and entropy inequalities, in settings with finite numbers of degrees of freedom. We will also introduce the Page curve and its significance. Finally, in the fourth lecture we will set up a toy model of the BHIP in Anti de Sitter space (AdS). Because AdS is believed to have a dual description as a conformal quantum field theory, we will use this duality to our advantage. We end with a broad discussion synthesizing what we have learned, and what is left to understand.
Posted by: andrea
January 2025
Wed
29 Jan 2025
From data to the analytic S-matrix
Andrea Guerrieri
(City University of London)
Abstract:
In this talk I will discuss our recent attempt https://arxiv.org/pdf/2410.23333 of understanding the QCD spectrum using the available experimental data.
To do so, we developed a fit strategy that combines the S-matrix Bootstrap with non-convex optimization methods, and applied our algorithm to the case of \pi\pi scattering.
The fitted amplitude correctly predicts the low energy ChiPT behavior, the experimental total cross sections at higher energy, and the physical spectrum up to 1.4 GeV. Surprisingly, Bootstrap predicts an additional tetraquark state, not yet observed, and that is being investigated in the decay of the B+ -> pi+ p+ pi- at LHCb.
In this talk I will discuss our recent attempt https://arxiv.org/pdf/2410.23333 of understanding the QCD spectrum using the available experimental data.
To do so, we developed a fit strategy that combines the S-matrix Bootstrap with non-convex optimization methods, and applied our algorithm to the case of \pi\pi scattering.
The fitted amplitude correctly predicts the low energy ChiPT behavior, the experimental total cross sections at higher energy, and the physical spectrum up to 1.4 GeV. Surprisingly, Bootstrap predicts an additional tetraquark state, not yet observed, and that is being investigated in the decay of the B+ -> pi+ p+ pi- at LHCb.
Posted by: IC2
Wed
29 Jan 2025
Classical Double Copy: Horizons, Penrose Limits, and Asymptotics
📍 London
Cynthia Keeler
(Arizona State U.)
Abstract:
I will briefly review the classical double copy, which maps exact solutions of classical gauge theories like electromagnetism, to solutions of general relativity. We will discuss why a position-space map is feasible, and then relate several gravitational objects (including horizons, Penrose limits, and asymptotics) to their gauge theory analogues.
I will briefly review the classical double copy, which maps exact solutions of classical gauge theories like electromagnetism, to solutions of general relativity. We will discuss why a position-space map is feasible, and then relate several gravitational objects (including horizons, Penrose limits, and asymptotics) to their gauge theory analogues.
Posted by: andrea
Mon
27 Jan 2025
Lonti: An introduction to the black hole information paradox (2/4)
Tarek Anous
(QMUL)
Abstract:
This course will give a technical introduction to the black hole information paradox (BHIP). In the first lecture, we will begin with a review of quantum path integrals, both in Lorentzian and in Euclidean signature. We will review the Euclidean path integral connection with statistical mechanics and thermodynamics while also reviewing the derivation of the first law of thermodynamics in standard equilibrium statistical mechanics. We will then introduce the laws of black hole thermodynamics, and study them in particular examples. The second lecture will be devoted to the Unruh effect. We will study free quantum field theory in Rindler space, which, locally, is the spacetime observed by a uniformly accelerated observer. We will derive that this observer measures a temperature related to the observer proper acceleration. The third lecture will be devoted to classical and quantum information theory including notions of conditional probability, mutual information, and entropy inequalities, in settings with finite numbers of degrees of freedom. We will also introduce the Page curve and its significance. Finally, in the fourth lecture we will set up a toy model of the BHIP in Anti de Sitter space (AdS). Because AdS is believed to have a dual description as a conformal quantum field theory, we will use this duality to our advantage. We end with a broad discussion synthesizing what we have learned, and what is left to understand.
This course will give a technical introduction to the black hole information paradox (BHIP). In the first lecture, we will begin with a review of quantum path integrals, both in Lorentzian and in Euclidean signature. We will review the Euclidean path integral connection with statistical mechanics and thermodynamics while also reviewing the derivation of the first law of thermodynamics in standard equilibrium statistical mechanics. We will then introduce the laws of black hole thermodynamics, and study them in particular examples. The second lecture will be devoted to the Unruh effect. We will study free quantum field theory in Rindler space, which, locally, is the spacetime observed by a uniformly accelerated observer. We will derive that this observer measures a temperature related to the observer proper acceleration. The third lecture will be devoted to classical and quantum information theory including notions of conditional probability, mutual information, and entropy inequalities, in settings with finite numbers of degrees of freedom. We will also introduce the Page curve and its significance. Finally, in the fourth lecture we will set up a toy model of the BHIP in Anti de Sitter space (AdS). Because AdS is believed to have a dual description as a conformal quantum field theory, we will use this duality to our advantage. We end with a broad discussion synthesizing what we have learned, and what is left to understand.
Posted by: andrea
Thu
23 Jan 2025
Critical QFTs with Spontaneously Broken Scale Symmetry
📍 London
Daniel Litim
(University of Sussex)
Abstract:
Scale symmetry is an important concept in quantum and statistical
physics. It arises at fixed points of the renormalisation group,
often alongside full conformal symmetry, and implies that theories
are massless with correlation functions given by universal numbers.
New phenomena arise when scale symmetry is broken spontaneously,
leading to a Goldstone boson, the dilaton, and the appearance of
a mass scale that is not determined by the fundamental parameters
of the theory. In this talk, I discuss scalar, fermionic, and
Yukawa theories in three dimensions, each with lines of strongly-coupled
conformal fixed points that terminate with spontaneous scale symmetry
breaking. Interrelations between models, dualities, and aspects of
dilaton physics are worked out from first principles. Further
implications for CFTs and model building are indicated.
Scale symmetry is an important concept in quantum and statistical
physics. It arises at fixed points of the renormalisation group,
often alongside full conformal symmetry, and implies that theories
are massless with correlation functions given by universal numbers.
New phenomena arise when scale symmetry is broken spontaneously,
leading to a Goldstone boson, the dilaton, and the appearance of
a mass scale that is not determined by the fundamental parameters
of the theory. In this talk, I discuss scalar, fermionic, and
Yukawa theories in three dimensions, each with lines of strongly-coupled
conformal fixed points that terminate with spontaneous scale symmetry
breaking. Interrelations between models, dualities, and aspects of
dilaton physics are worked out from first principles. Further
implications for CFTs and model building are indicated.
Posted by: QMW
Wed
22 Jan 2025
Holographic correlators with 1/2-BPS bound states
Rodolfo Russo
(QMUL)
Abstract:
In the AdS/CFT context, 1/2-BPS asymptotically AdS supergravity solutions can be used to derive holographic 4-point correlators. Beside reproducing known strong-coupling results for the 4-point correlators with single particle states, this approach can be used to derive new 4-point correlators with two single particle and two multiparticle states. I will provide some explicit examples of these correlators with double-particle states both in AdS3 and AdS5. The results can be written in terms of a natural generalisation of the usual D-functions appearing in the 4-point correlators with single particle states.
In the AdS/CFT context, 1/2-BPS asymptotically AdS supergravity solutions can be used to derive holographic 4-point correlators. Beside reproducing known strong-coupling results for the 4-point correlators with single particle states, this approach can be used to derive new 4-point correlators with two single particle and two multiparticle states. I will provide some explicit examples of these correlators with double-particle states both in AdS3 and AdS5. The results can be written in terms of a natural generalisation of the usual D-functions appearing in the 4-point correlators with single particle states.
Posted by: IC2
Wed
22 Jan 2025
Holographic correlators with 1/2-BPS bound states
Rodolfo Russo
(QMUL)
Abstract:
In the AdS/CFT context, 1/2-BPS asymptotically AdS supergravity solutions can be used to derive holographic 4-point correlators. Beside reproducing known strong-coupling results for the 4-point correlators with single particle states, this approach can be used to derive new 4-point correlators with two single particle and two multiparticle states. I will provide some explicit examples of these correlators with double-particle states both in AdS3 and AdS5. The results can be written in terms of a natural generalisation of the usual D-functions appearing in the 4-point correlators with single particle states.
In the AdS/CFT context, 1/2-BPS asymptotically AdS supergravity solutions can be used to derive holographic 4-point correlators. Beside reproducing known strong-coupling results for the 4-point correlators with single particle states, this approach can be used to derive new 4-point correlators with two single particle and two multiparticle states. I will provide some explicit examples of these correlators with double-particle states both in AdS3 and AdS5. The results can be written in terms of a natural generalisation of the usual D-functions appearing in the 4-point correlators with single particle states.
Posted by: IC2
Wed
22 Jan 2025
From Categories to Cold Atoms: Phases of Matter from new Symmetries
📍 London
Sakura Schafer-Nameki
(Oxford U.)
Abstract:
I will explain how the recent developments in so-called categorical or non-invertible symmetries can be used to make sharp predictions about phases – gapped and gapless – in the presence of such symmetries. This so-called a categorical Landau paradigm applied to 1+1d systems predicts new phases and phase transitions. In some instances these are extremely simple to implement in spin-chains and have a potential to be implemented in the very near future in cold atom systems
I will explain how the recent developments in so-called categorical or non-invertible symmetries can be used to make sharp predictions about phases – gapped and gapless – in the presence of such symmetries. This so-called a categorical Landau paradigm applied to 1+1d systems predicts new phases and phase transitions. In some instances these are extremely simple to implement in spin-chains and have a potential to be implemented in the very near future in cold atom systems
Posted by: andrea
Mon
20 Jan 2025
Lonti: An introduction to the black hole information paradox (1/4)
Tarek Anous
(QMUL)
Abstract:
This course will give a technical introduction to the black hole information paradox (BHIP). In the first lecture, we will begin with a review of quantum path integrals, both in Lorentzian and in Euclidean signature. We will review the Euclidean path integral connection with statistical mechanics and thermodynamics while also reviewing the derivation of the first law of thermodynamics in standard equilibrium statistical mechanics. We will then introduce the laws of black hole thermodynamics, and study them in particular examples. The second lecture will be devoted to the Unruh effect. We will study free quantum field theory in Rindler space, which, locally, is the spacetime observed by a uniformly accelerated observer. We will derive that this observer measures a temperature related to the observer proper acceleration. The third lecture will be devoted to classical and quantum information theory including notions of conditional probability, mutual information, and entropy inequalities, in settings with finite numbers of degrees of freedom. We will also introduce the Page curve and its significance. Finally, in the fourth lecture we will set up a toy model of the BHIP in Anti de Sitter space (AdS). Because AdS is believed to have a dual description as a conformal quantum field theory, we will use this duality to our advantage. We end with a broad discussion synthesizing what we have learned, and what is left to understand.
This course will give a technical introduction to the black hole information paradox (BHIP). In the first lecture, we will begin with a review of quantum path integrals, both in Lorentzian and in Euclidean signature. We will review the Euclidean path integral connection with statistical mechanics and thermodynamics while also reviewing the derivation of the first law of thermodynamics in standard equilibrium statistical mechanics. We will then introduce the laws of black hole thermodynamics, and study them in particular examples. The second lecture will be devoted to the Unruh effect. We will study free quantum field theory in Rindler space, which, locally, is the spacetime observed by a uniformly accelerated observer. We will derive that this observer measures a temperature related to the observer proper acceleration. The third lecture will be devoted to classical and quantum information theory including notions of conditional probability, mutual information, and entropy inequalities, in settings with finite numbers of degrees of freedom. We will also introduce the Page curve and its significance. Finally, in the fourth lecture we will set up a toy model of the BHIP in Anti de Sitter space (AdS). Because AdS is believed to have a dual description as a conformal quantum field theory, we will use this duality to our advantage. We end with a broad discussion synthesizing what we have learned, and what is left to understand.
Posted by: andrea
Mon
20 Jan 2025
An Exact Solution to the Navier-Stokes Equations for Decaying Turbulence: Universal Results from First Principles.
Alexander Migdal
(IAS, Princeton)
Abstract:
Decaying turbulence, characterized by energy dissipation from an initial high-energy state, remains a fundamental challenge in classical physics. This work presents an exact analytical solution to the Navier-Stokes (NS) equations for incompressible fluid flow in the context of decaying turbulence, introducing the novel framework of the Euler ensemble. This framework maps turbulent dynamics onto discrete states represented by regular star polygons with rational vertex angles in units of 2π.
A key feature of the Euler ensemble is a duality between classical turbulence and a hidden one-dimensional quantum system, analogous to the AdS/CFT correspondence in quantum field theory. This duality enables the derivation of exact turbulence statistics, replacing traditional heuristic scaling laws with universal results derived directly from the NS equations. For example, the decay law for turbulent kinetic energy is predicted as \( E(t)∼t^{−5/4}\), with quantitative agreement to within 1% standard deviation in experimental and numerical data.
The framework is validated using Direct Numerical Simulations (DNS) and experimental results, including grid turbulence and large-tank experiments. Additionally, the Euler ensemble predicts novel macroscopic quantum-like effects, such as oscillations in the decay index as a function of the scaling variable \(r/\sqrt t\). These predictions highlight new avenues for experimental and numerical exploration of turbulence.
This work addresses long-standing challenges in turbulence theory, providing a rigorous, universal description of decaying turbulence with applications across fluid dynamics, geophysics, and engineering.
Decaying turbulence, characterized by energy dissipation from an initial high-energy state, remains a fundamental challenge in classical physics. This work presents an exact analytical solution to the Navier-Stokes (NS) equations for incompressible fluid flow in the context of decaying turbulence, introducing the novel framework of the Euler ensemble. This framework maps turbulent dynamics onto discrete states represented by regular star polygons with rational vertex angles in units of 2π.
A key feature of the Euler ensemble is a duality between classical turbulence and a hidden one-dimensional quantum system, analogous to the AdS/CFT correspondence in quantum field theory. This duality enables the derivation of exact turbulence statistics, replacing traditional heuristic scaling laws with universal results derived directly from the NS equations. For example, the decay law for turbulent kinetic energy is predicted as \( E(t)∼t^{−5/4}\), with quantitative agreement to within 1% standard deviation in experimental and numerical data.
The framework is validated using Direct Numerical Simulations (DNS) and experimental results, including grid turbulence and large-tank experiments. Additionally, the Euler ensemble predicts novel macroscopic quantum-like effects, such as oscillations in the decay index as a function of the scaling variable \(r/\sqrt t\). These predictions highlight new avenues for experimental and numerical exploration of turbulence.
This work addresses long-standing challenges in turbulence theory, providing a rigorous, universal description of decaying turbulence with applications across fluid dynamics, geophysics, and engineering.
Posted by: oxford
Wed
15 Jan 2025
Exploring Confinement in Anti-de Sitter Space
📍 London
Marco Serone
(SISSA)
Abstract:
The study of non-abelian gauge theories in compact or non-flat spaces can be useful to gather insights and new perspectives on the confinement problem. We consider Yang-Mills theory on four dimensional Anti-de Sitter space and wonder how signals of confinement in the bulk can be detected from boundary observables. The Dirichlet boundary condition cannot exist at arbitrarily large radius because it would give rise to colored asymptotic states in flat space and hence a deconfinement-confinement transition has to occur as the radius is increased. By perturbative computations we provide evidence for the scenario of merger and annihilation. Namely, the theory with Dirichlet boundary condition stops existing because it merges and annihilates with another theory. We also derive a general result for the leading-order anomalous dimension of the so called displacement operator for a generic perturbation in Anti-de Sitter, showing that it is related to the beta function of bulk couplings.
The study of non-abelian gauge theories in compact or non-flat spaces can be useful to gather insights and new perspectives on the confinement problem. We consider Yang-Mills theory on four dimensional Anti-de Sitter space and wonder how signals of confinement in the bulk can be detected from boundary observables. The Dirichlet boundary condition cannot exist at arbitrarily large radius because it would give rise to colored asymptotic states in flat space and hence a deconfinement-confinement transition has to occur as the radius is increased. By perturbative computations we provide evidence for the scenario of merger and annihilation. Namely, the theory with Dirichlet boundary condition stops existing because it merges and annihilates with another theory. We also derive a general result for the leading-order anomalous dimension of the so called displacement operator for a generic perturbation in Anti-de Sitter, showing that it is related to the beta function of bulk couplings.
Posted by: andrea
Wed
15 Jan 2025
Exploring doubly-holographic BCFTs
Christoph Uhlemann
(Vrije Universiteit Brussel)
Abstract:
I will discuss recent work on N=4 SYM with Gaiotto-Witten boundaries, defects and interfaces. This broad class of theories with its high degree of supersymmetry and rich defect dynamics is a natural laboratory for exploring the physics of boundaries and defects, and it contains boundary conformal field theories that underlie string theory realizations of double holography. We will discuss a tight interplay between the holographic duals of these theories and the matrix models arising from supersymmetric localization, defect one-point functions, and large-charge operators.
I will discuss recent work on N=4 SYM with Gaiotto-Witten boundaries, defects and interfaces. This broad class of theories with its high degree of supersymmetry and rich defect dynamics is a natural laboratory for exploring the physics of boundaries and defects, and it contains boundary conformal field theories that underlie string theory realizations of double holography. We will discuss a tight interplay between the holographic duals of these theories and the matrix models arising from supersymmetric localization, defect one-point functions, and large-charge operators.
Posted by: IC2