Triangle Seminars
December 2025
Wed
17 Dec 2025
Black hole interiors, arithmetic chaos and primon gases
📍 London
Marine De Clerck
(Cambridge University)
Abstract:
Seminal work by Belinskii, Khalatnikov, Lifshitz (BKL) and others some 50 years ago lead to an analytic understanding of the generic behaviour of solutions to Einstein’s equations in the approach to certain cosmological singularities. The dynamics is chaotic and can elegantly be reformulated in terms of `cosmological billiards’, in which the peculiar symmetries of the model become apparent, with deep connections to number theory. In this talk, I want to give an overview of recent progress in this direction.
Seminal work by Belinskii, Khalatnikov, Lifshitz (BKL) and others some 50 years ago lead to an analytic understanding of the generic behaviour of solutions to Einstein’s equations in the approach to certain cosmological singularities. The dynamics is chaotic and can elegantly be reformulated in terms of `cosmological billiards’, in which the peculiar symmetries of the model become apparent, with deep connections to number theory. In this talk, I want to give an overview of recent progress in this direction.
Posted by: Andrew Svesko
Mon
15 Dec 2025
A relationship between gauge theories with finite and continuous gauge groups
📍 London
Pavel Putrov
(ICTP)
Abstract:
In my talk, I will discuss certain relations between 3-dimensional
topological gauge theories with continuous and finite gauge groups,
commonly known as Chern-Simons and Dijkgraaf-Witten theories
respectively. The relations of this form appear when the continuous and
finite gauge groups are the same algebraic group considered over complex
numbers or a finite field respectively. In this talk I will focus on the
SU(2) example.
Please look at other details on our web post https://lims.ac.uk/
In my talk, I will discuss certain relations between 3-dimensional
topological gauge theories with continuous and finite gauge groups,
commonly known as Chern-Simons and Dijkgraaf-Witten theories
respectively. The relations of this form appear when the continuous and
finite gauge groups are the same algebraic group considered over complex
numbers or a finite field respectively. In this talk I will focus on the
SU(2) example.
Please look at other details on our web post https://lims.ac.uk/
Posted by: JUVEN WANG
Thu
11 Dec 2025
One Constant to Rule Them All
📍 London
Ekaterina Sysoeva
(Turin)
Abstract:
The SU(N) theory with 2N fundamental matter multiplets, in the vicinity of the so-called special vacuum - where the vacuum expectation values of the Higgs field are arranged near the vertices of a regular N-gon - is known to possess ⌊N/2⌋ effective coupling constants. I will show, however, that with the diameter of the polygon tending to infinity, a single effective coupling constant emerges. Moreover, this unique effective coupling enters the Zamolodchikov-like recurrence relation for the instanton partition function that remains valid for arbitrary vacuum expectation values, and is therefore meaningful beyond the special vacuum. By reconstructing the coupling matrix with simple symmetry and dimensional arguments, I will clarify the origin of this unique effective coupling. Finally, I will present the complete set of ⌊N/2⌋ effective couplings and discuss their modular properties, as well as the corrections induced by the masses of the matter multiplets.
The SU(N) theory with 2N fundamental matter multiplets, in the vicinity of the so-called special vacuum - where the vacuum expectation values of the Higgs field are arranged near the vertices of a regular N-gon - is known to possess ⌊N/2⌋ effective coupling constants. I will show, however, that with the diameter of the polygon tending to infinity, a single effective coupling constant emerges. Moreover, this unique effective coupling enters the Zamolodchikov-like recurrence relation for the instanton partition function that remains valid for arbitrary vacuum expectation values, and is therefore meaningful beyond the special vacuum. By reconstructing the coupling matrix with simple symmetry and dimensional arguments, I will clarify the origin of this unique effective coupling. Finally, I will present the complete set of ⌊N/2⌋ effective couplings and discuss their modular properties, as well as the corrections induced by the masses of the matter multiplets.
Posted by: Nathan Moynihan
Thu
11 Dec 2025
Quantum Integrable Systems: From Bethe Ansatz to Langlands Duality
📍 London
Edward Frenkel
(UC Berkeley)
Abstract:
I will present some recent results on quantum integrable systems, such as the Gaudin model, the XXZ model, and their generalizations to all affine Kac-Moody algebras and their quantum deformations (quantum affine algebras). I will also explain how the problem of finding the spectra of the Hamiltonians in these models is connected to the geometric Langlands correspondence and the theory of q-characters of quantum affine algebras. This gives a new perspective on (and substitutes) the old method for finding these spectra, the Bethe Ansatz.
I will present some recent results on quantum integrable systems, such as the Gaudin model, the XXZ model, and their generalizations to all affine Kac-Moody algebras and their quantum deformations (quantum affine algebras). I will also explain how the problem of finding the spectra of the Hamiltonians in these models is connected to the geometric Langlands correspondence and the theory of q-characters of quantum affine algebras. This gives a new perspective on (and substitutes) the old method for finding these spectra, the Bethe Ansatz.
Posted by: Evgeny Sobko
Wed
10 Dec 2025
Generalized Families of QFTs
📍 London
Daniel Brennan
(University of Birmingham)
Abstract:
In this talk we introduce the notion of generalized/categorical families of QFTs. These families of theories have a structure which is analogous to the categorical symmetries in Lagrangian QFTs and may be thought of as the family structure that arises when a categorical symmetry is explicitly broken by deformations of the action. After describing this structure, we will explain the anomalies of these families and their implications. We will then use this structure to study some higher dimensional deformations of 4d N=1 SUSY gauge theories.
In this talk we introduce the notion of generalized/categorical families of QFTs. These families of theories have a structure which is analogous to the categorical symmetries in Lagrangian QFTs and may be thought of as the family structure that arises when a categorical symmetry is explicitly broken by deformations of the action. After describing this structure, we will explain the anomalies of these families and their implications. We will then use this structure to study some higher dimensional deformations of 4d N=1 SUSY gauge theories.
Posted by: Andrew Svesko
Wed
10 Dec 2025
A topological proof of the \(H\)-colouring dichotomy
📍 East of England
Jakub Opršal
(University of Birmingham)
Abstract:
A colouring of a graph with \(k\) colours is an assignment of colours to vertices so that no edge is monochromatic. As it is well-known colouring with 2 colours is in P while colouring with \(k > 2\) colours is NP-complete. This dichotomy was extended to the *graph homomorphism problem*, also called \(H\)-colouring, by Hell and Nešetřil [J. Comb. Theory B, 48(1):92-110, 1990]. More precisely, they proved that deciding whether there is a graph homomorphism from a given graph to a fixed graph \(H\) is in P if \(H\) is bipartite (or contains a self-loop), and is NP-complete otherwise. This dichotomy served as an important test-case for the Feder–Vardi dichotomy conjecture, and Bulatov–Zhuk dichotomy of complexity of finite-template CSPs.
In the talk, I will present a new proof of this theorem using tools from topological combinatorics based on ideas of Lovász [J. Comb. Theory, Ser. A, 25(3):319-324, 1978] and Brower’s fixed-point theorem. This is joint work with Sebastian Meyer (TU Dresden).
A colouring of a graph with \(k\) colours is an assignment of colours to vertices so that no edge is monochromatic. As it is well-known colouring with 2 colours is in P while colouring with \(k > 2\) colours is NP-complete. This dichotomy was extended to the *graph homomorphism problem*, also called \(H\)-colouring, by Hell and Nešetřil [J. Comb. Theory B, 48(1):92-110, 1990]. More precisely, they proved that deciding whether there is a graph homomorphism from a given graph to a fixed graph \(H\) is in P if \(H\) is bipartite (or contains a self-loop), and is NP-complete otherwise. This dichotomy served as an important test-case for the Feder–Vardi dichotomy conjecture, and Bulatov–Zhuk dichotomy of complexity of finite-template CSPs.
In the talk, I will present a new proof of this theorem using tools from topological combinatorics based on ideas of Lovász [J. Comb. Theory, Ser. A, 25(3):319-324, 1978] and Brower’s fixed-point theorem. This is joint work with Sebastian Meyer (TU Dresden).
Posted by: Julian Kupka
Tue
9 Dec 2025
Phases of 2d Gauge Theories and Symmetric Mass Generation
📍 London
Rishi Mouland
(Imperial College)
Abstract:
I will review the motivation and aims of symmetric mass generation (SMG), whereby fermions are gapped while preserving a chiral but necessarily non-anomalous symmetry. A simple model of SMG will be described, which leverages strongly-coupled gauge dynamics. I will then use CFT tools alongside bosonisation to derive the phase diagrams of a series of 2d Abelian gauge theories, including the 2d SMG model, in doing so establishing its validity. I will finally comment on the application of such constructions to symmetry-preserving boundary conditions and fermion-monopole scattering in 4d gauge theory.
I will review the motivation and aims of symmetric mass generation (SMG), whereby fermions are gapped while preserving a chiral but necessarily non-anomalous symmetry. A simple model of SMG will be described, which leverages strongly-coupled gauge dynamics. I will then use CFT tools alongside bosonisation to derive the phase diagrams of a series of 2d Abelian gauge theories, including the 2d SMG model, in doing so establishing its validity. I will finally comment on the application of such constructions to symmetry-preserving boundary conditions and fermion-monopole scattering in 4d gauge theory.
Posted by: João Vilas Boas
Tue
9 Dec 2025
String scattering old and new
📍 London
Axel Kleinschmidt
(AEI)
Abstract:
String theory was arguably born with a scattering amplitude in 1968, and the formula came before its derivation. I will review the many aspects of scattering amplitudes in string theory with the aim of illustrating some of the recent advances. These combine insights from physics and mathematics and shine new light on these central observables and how they connect with quantum field theory
String theory was arguably born with a scattering amplitude in 1968, and the formula came before its derivation. I will review the many aspects of scattering amplitudes in string theory with the aim of illustrating some of the recent advances. These combine insights from physics and mathematics and shine new light on these central observables and how they connect with quantum field theory
Posted by: Sebastian Cespedes
Mon
8 Dec 2025
String Data
📍 London
Multiple Multiple
Abstract:
https://indico.global/event/14913/
https://indico.global/event/14913/
Posted by: Yang-Hui He
Thu
4 Dec 2025
Energy Correlators in CFTs
📍 London
Matthew Walters
(Heriot Watt)
Abstract:
One useful observable for studying QFT dynamics is the correlation between the total energy flux in different directions on the celestial sphere. I will discuss the computation of these energy correlators in the specific case of conformal field theories, where they can be obtained as a sum over conformal blocks. After reviewing some general properties of energy correlators in CFTs, I will show how they can be used to derive novel bounds on OPE coefficients involving the stress-energy tensor.
One useful observable for studying QFT dynamics is the correlation between the total energy flux in different directions on the celestial sphere. I will discuss the computation of these energy correlators in the specific case of conformal field theories, where they can be obtained as a sum over conformal blocks. After reviewing some general properties of energy correlators in CFTs, I will show how they can be used to derive novel bounds on OPE coefficients involving the stress-energy tensor.
Posted by: Nathan Moynihan
Wed
3 Dec 2025
Dualities in supersymmetric quantum mechanics (and DT4 invariants from graded quivers)
📍 London
Cyril Closset
(Birmingham University)
Abstract:
I will discuss Seiberg-like dualities of N=2 supersymmetric quantum mechanics (SQM), emphasizing new aspects compared to dualities of 2d N=(0,2) gauge theories. In particular, I will present new mutation dualities for 1d N=2 SQCD with unitary gauge group. I will also comment on the relationship between 1d N=2 quivers and DT4 invariants of local fourfolds.
I will discuss Seiberg-like dualities of N=2 supersymmetric quantum mechanics (SQM), emphasizing new aspects compared to dualities of 2d N=(0,2) gauge theories. In particular, I will present new mutation dualities for 1d N=2 SQCD with unitary gauge group. I will also comment on the relationship between 1d N=2 quivers and DT4 invariants of local fourfolds.
Posted by: Jesse van Muiden
Wed
3 Dec 2025
Some universality in brane scattering
📍 London
Congkao Wen
(Queen Mary University London)
Abstract:
In this talk, I will discuss some features of heavy–heavy–light–light correlators in N=4 supersymmetric Yang–Mills theory, where the light operators belong to the stress-tensor multiplet and the heavy ones correspond to giant gravitons, realised holographically as D3-branes. I will focus on the associated Integrated Correlators, for which exact expressions can be obtained despite few results are known for the correlators themselves. I will highlight several interesting properties of these integrated correlators, especially the emergence of universal structures in the strong-coupling regime. I will also discuss different integrated correlators in certain N=2 superconformal field theories, which are holographically dual to scattering of gravitons (and gluons) in the presence of D7-branes. Surprisingly, these integrated correlators in N=2 theories are given by exactly the same strong coupling asymptotic series as those of giant gravitons, despite the fact that their weak coupling expansions are very different.
In this talk, I will discuss some features of heavy–heavy–light–light correlators in N=4 supersymmetric Yang–Mills theory, where the light operators belong to the stress-tensor multiplet and the heavy ones correspond to giant gravitons, realised holographically as D3-branes. I will focus on the associated Integrated Correlators, for which exact expressions can be obtained despite few results are known for the correlators themselves. I will highlight several interesting properties of these integrated correlators, especially the emergence of universal structures in the strong-coupling regime. I will also discuss different integrated correlators in certain N=2 superconformal field theories, which are holographically dual to scattering of gravitons (and gluons) in the presence of D7-branes. Surprisingly, these integrated correlators in N=2 theories are given by exactly the same strong coupling asymptotic series as those of giant gravitons, despite the fact that their weak coupling expansions are very different.
Posted by: Andrew Svesko
Wed
3 Dec 2025
The magic of scattering amplitudes
📍 East of England
Chris White
(Queen Mary University of London)
Abstract:
In recent years, a growing community of researchers have been applying ideas from Quantum Information / Computing theory to high energy physics. Entanglement is one such quantity, but there are by now many others. This talk will examine the property of “magic” (also known as “non-stabliserness”) which, roughly speaking, measures whether quantum systems have a genuine computational advantage over their classical counterparts. I will review the origin of this concept, before describing recent applications from both collider physics and scattering amplitudes research. No prior knowledge of quantum computing will be assumed.
In recent years, a growing community of researchers have been applying ideas from Quantum Information / Computing theory to high energy physics. Entanglement is one such quantity, but there are by now many others. This talk will examine the property of “magic” (also known as “non-stabliserness”) which, roughly speaking, measures whether quantum systems have a genuine computational advantage over their classical counterparts. I will review the origin of this concept, before describing recent applications from both collider physics and scattering amplitudes research. No prior knowledge of quantum computing will be assumed.
Posted by: Julian Kupka
November 2025
Thu
27 Nov 2025
A first look at hexagonal bootstrap for QCD scattering amplitudes
📍 London
Qinglin Yang
(Max Planck Inst.)
Abstract:
In this talk, we present a bootstrap construction of planar two-loop
six-point scattering amplitudes in QCD theory, focusing on their maximal
transcendental weight components. From an analysis of on-shell diagrams,
we identify a complete and conformally-invariant set of leading
singularities. Combining these results with recent advances in
understanding the relevant hexagonal function space from canonical
differential equation, we can uniquely determine the maximal weight
parts of helicity amplitudes by imposing correct physical limits. We
especially present a detailed picture of two-loop six-point amplitudes
at the symbol level in pure Yang–Mills theory. It also reveals a
remarkably small and tightly constrained function alphabet, hinting at a
deeper organizing principle similar to that observed in maximally
supersymmetric Yang–Mills theory.
In this talk, we present a bootstrap construction of planar two-loop
six-point scattering amplitudes in QCD theory, focusing on their maximal
transcendental weight components. From an analysis of on-shell diagrams,
we identify a complete and conformally-invariant set of leading
singularities. Combining these results with recent advances in
understanding the relevant hexagonal function space from canonical
differential equation, we can uniquely determine the maximal weight
parts of helicity amplitudes by imposing correct physical limits. We
especially present a detailed picture of two-loop six-point amplitudes
at the symbol level in pure Yang–Mills theory. It also reveals a
remarkably small and tightly constrained function alphabet, hinting at a
deeper organizing principle similar to that observed in maximally
supersymmetric Yang–Mills theory.
Posted by: Nathan Moynihan
Wed
26 Nov 2025
CANCELLED: Unitarity constraints of four-dimensional conformal theories with 8 supercharges
📍 London
Madalena Lemos
(Durham University)
Abstract:
We review a construction of two-dimensional chiral algebras inside four-dimensional conformal theories with 8 or more supercharges. While the chiral algebra is not unitarity, it inherits an extra structure from the fact that the parent four-dimensional theory is unitarity. We discuss this extra structure and use it to obtain constraints on which chiral algebras arise from four dimensions, as well as constraints on four-dimensional theories.
We review a construction of two-dimensional chiral algebras inside four-dimensional conformal theories with 8 or more supercharges. While the chiral algebra is not unitarity, it inherits an extra structure from the fact that the parent four-dimensional theory is unitarity. We discuss this extra structure and use it to obtain constraints on which chiral algebras arise from four dimensions, as well as constraints on four-dimensional theories.
Posted by: Jesse van Muiden
Wed
26 Nov 2025
Holographic correlators with 1/2-BPS bound states
📍 London
Rodolfo Russo
(Queen Mary University London)
Abstract:
In holographic CFT's, such as N=4 SYM, it is natural to organise the spectrum in single and multi particle states. By now we have a wealth of information about 4-point correlators with BPS single particle states, but much less is known about 4-point correlators involving multi particle states. I will discuss how we can calculate such correlators at strong coupling by using various techniques: bootstrap, OPE's of higher point functions and a bulk approach based on 1/2-BPS asymptotically AdS supergravity solutions. I will provide explicit results for various families of 4-point correlators with one or two 1/2-BPS multi particle states in the context of the AdS5/N=4 SYM duality.
In holographic CFT's, such as N=4 SYM, it is natural to organise the spectrum in single and multi particle states. By now we have a wealth of information about 4-point correlators with BPS single particle states, but much less is known about 4-point correlators involving multi particle states. I will discuss how we can calculate such correlators at strong coupling by using various techniques: bootstrap, OPE's of higher point functions and a bulk approach based on 1/2-BPS asymptotically AdS supergravity solutions. I will provide explicit results for various families of 4-point correlators with one or two 1/2-BPS multi particle states in the context of the AdS5/N=4 SYM duality.
Posted by: Andrew Svesko
Wed
26 Nov 2025
Varieties of gauge theories
📍 East of England
Ben Gripaios
(University of Cambridge)
Abstract:
I will describe the use of methods of arithmetic geometry to find gauge theories in 4 dimensions that are free of anomalies. In many cases, it is possible to find all such theories.
I will describe the use of methods of arithmetic geometry to find gauge theories in 4 dimensions that are free of anomalies. In many cases, it is possible to find all such theories.
Posted by: Julian Kupka
Tue
25 Nov 2025
Conserved Currents and Bilinear Forms for Quasinormal Modes in the Hyperboloidal Formalism
📍 London
Marica Minucci
(Niels Bohr Institute, University of Copenhagen)
Abstract:
The late-time gravitational-wave signal from a binary black hole merger is dominated by quasinormal ringing, a spectrum of damped oscillations whose complex frequencies, in linear perturbation theory, depend only on the remnant’s mass and spin. These modes encode a unique spectral fingerprint of the final black hole, and current observations already hint at the presence of overtones.
To fully exploit these signals, we must develop a framework for quasinormal mode (QNM) interactions. The ringdown follows a highly nonlinear merger phase, and although numerical simulations suggest that a linear superposition of modes models the signal well, the connection to a fully nonlinear description remains unclear. A key difficulty is that Kerr QNMs do not form a complete orthogonal basis. Moreover, their spatial wavefunctions diverge at both the bifurcation sphere and spatial infinity, complicating the construction of canonical inner products on standard Cauchy hypersurfaces. Thus, it remains unclear how to project onto QNMs to study nonlinear mode mixing. In this talk, I will present bilinear forms that serve as inner-product analogues for Weyl scalars, constructed from conserved currents and symmetry operators. I will discuss their key properties on hyperboloidal slices, using the Schwarzschild spacetime as a model example. This work is in collaboration with Rodrigo Panosso Macedo, Christiana Pantelidou, and Laura Sberna.
The late-time gravitational-wave signal from a binary black hole merger is dominated by quasinormal ringing, a spectrum of damped oscillations whose complex frequencies, in linear perturbation theory, depend only on the remnant’s mass and spin. These modes encode a unique spectral fingerprint of the final black hole, and current observations already hint at the presence of overtones.
To fully exploit these signals, we must develop a framework for quasinormal mode (QNM) interactions. The ringdown follows a highly nonlinear merger phase, and although numerical simulations suggest that a linear superposition of modes models the signal well, the connection to a fully nonlinear description remains unclear. A key difficulty is that Kerr QNMs do not form a complete orthogonal basis. Moreover, their spatial wavefunctions diverge at both the bifurcation sphere and spatial infinity, complicating the construction of canonical inner products on standard Cauchy hypersurfaces. Thus, it remains unclear how to project onto QNMs to study nonlinear mode mixing. In this talk, I will present bilinear forms that serve as inner-product analogues for Weyl scalars, constructed from conserved currents and symmetry operators. I will discuss their key properties on hyperboloidal slices, using the Schwarzschild spacetime as a model example. This work is in collaboration with Rodrigo Panosso Macedo, Christiana Pantelidou, and Laura Sberna.
Posted by: João Vilas Boas
Tue
25 Nov 2025
Hyperbolic Mass in 2+1 Dimensions
📍 London
Raphaela Wutte
(University of Southampton)
Abstract:
Solutions to general relativity with a negative cosmological constant have received significant attention due to the conjectured AdS/CFT correspondence, a particularly well-understood example of which is exhibited in 2+1 dimensions.
I will review known vacuum solutions to general relativity with a negative cosmological constant in 2+1 dimensions and discuss the difficulties in defining mass, which are resolved via minimisation using a positive energy theorem. I will present a gluing theorem for vacuum time-symmetric general-relativistic initial data sets in two spatial dimensions. By gluing two given time-symmetric vacuum initial data sets at conformal infinity, we obtain new time-symmetric vacuum initial data sets. I will sketch the derivation of the mass formulae of the resulting manifolds. Our gluing theorem yields complete manifolds with any mass aspect function, which are smooth except for one conical singularity.
Solutions to general relativity with a negative cosmological constant have received significant attention due to the conjectured AdS/CFT correspondence, a particularly well-understood example of which is exhibited in 2+1 dimensions.
I will review known vacuum solutions to general relativity with a negative cosmological constant in 2+1 dimensions and discuss the difficulties in defining mass, which are resolved via minimisation using a positive energy theorem. I will present a gluing theorem for vacuum time-symmetric general-relativistic initial data sets in two spatial dimensions. By gluing two given time-symmetric vacuum initial data sets at conformal infinity, we obtain new time-symmetric vacuum initial data sets. I will sketch the derivation of the mass formulae of the resulting manifolds. Our gluing theorem yields complete manifolds with any mass aspect function, which are smooth except for one conical singularity.
Posted by: João Vilas Boas
Tue
25 Nov 2025
From Quantum Fluctuations to Cosmic Ripples: Gravitational Waves from Inflation
📍 London
Emanuela Dimastrogiovanni
(Groeningen University)
Abstract:
Primordial gravitational waves offer a rare opportunity to probe physics at energies far beyond the reach of terrestrial experiments, opening a unique window onto the very early universe. In this talk, I will explore how inflationary models beyond the simplest single-field picture can generate distinctive gravitational-wave signatures, and what this means for testing inflation with current and future interferometers. I will also discuss how anisotropies in the gravitational-wave energy density could become a powerful new probe of the inflationary era, with the potential to disentangle an inflationary background from those produced by other cosmic processes.
Primordial gravitational waves offer a rare opportunity to probe physics at energies far beyond the reach of terrestrial experiments, opening a unique window onto the very early universe. In this talk, I will explore how inflationary models beyond the simplest single-field picture can generate distinctive gravitational-wave signatures, and what this means for testing inflation with current and future interferometers. I will also discuss how anisotropies in the gravitational-wave energy density could become a powerful new probe of the inflationary era, with the potential to disentangle an inflationary background from those produced by other cosmic processes.
Posted by: Sebastian Cespedes
Tue
25 Nov 2025
Galois groups of random polynomials
📍 London
Manjul Bhargava
(IAS, Princeton)
Abstract:
Fields Medalist Prof. Manjul Bhargava will give a talk on his recent proof of van der Waerden's Conjecture.
Fields Medalist Prof. Manjul Bhargava will give a talk on his recent proof of van der Waerden's Conjecture.
Posted by: Yang-Hui He
Fri
21 Nov 2025
Tensor Models, 3d Gravity and Simplicial Decomposition
📍 London
Daniel L. Jafferis
(Harvard University, USA)
Abstract:
I will review the tensor/matrix model for 2d CFT data subject to crossing constraints, whose topological expansion is proposed to match that of pure 3d gravity. I will discuss various sources of divergences and what remains to prove the correspondence. Then I will turn to a BCFT extension of the model, particularly as associated to a purely open version of the bootstrap. I will explain how the resulting topological expansion is related to gluing tetrahedra, and show how the matrix model captures certain off-shell 3d gravity amplitudes.
Also posted on https://lims.ac.uk/ for more seminar info.
I will review the tensor/matrix model for 2d CFT data subject to crossing constraints, whose topological expansion is proposed to match that of pure 3d gravity. I will discuss various sources of divergences and what remains to prove the correspondence. Then I will turn to a BCFT extension of the model, particularly as associated to a purely open version of the bootstrap. I will explain how the resulting topological expansion is related to gluing tetrahedra, and show how the matrix model captures certain off-shell 3d gravity amplitudes.
Also posted on https://lims.ac.uk/ for more seminar info.
Posted by: JUVEN WANG
Wed
19 Nov 2025
A New Superstring Field Theory Action
📍 London
Chris Hull
(Imperial College London)
Abstract:
Sen’s superstring field theory successfully formulates perturbative superstring theory but has a number of strange features.
The action is not fully background independent, and it does not have standard diffeomorphism symmetry - instead there is an exotic gauge symmetry that acts on some fields but not others. These issues greatly restrict the spacetimes that this action can be applied to. A new action is found that reduces to Sen’s in a certain limit, but which has diffeomorphism symmetry together with further exotic symmetries and is background independent. As a result, it can be applied to any spacetime.
Sen’s superstring field theory successfully formulates perturbative superstring theory but has a number of strange features.
The action is not fully background independent, and it does not have standard diffeomorphism symmetry - instead there is an exotic gauge symmetry that acts on some fields but not others. These issues greatly restrict the spacetimes that this action can be applied to. A new action is found that reduces to Sen’s in a certain limit, but which has diffeomorphism symmetry together with further exotic symmetries and is background independent. As a result, it can be applied to any spacetime.
Posted by: Jesse van Muiden
Wed
19 Nov 2025
Quantum superstrings and supermembranes, and AdS/CFT
📍 London
Arkady Tseytlin
(Imperial College London)
Abstract:
I will review some results on semi-classical quantization of M2 branes in AdS4 x S7/Zk in their relation to dual ABJM theory and then discuss recent work on computing 2-loop corrections to world-volume S-matrix in superstring and supermembrane theory.
I will review some results on semi-classical quantization of M2 branes in AdS4 x S7/Zk in their relation to dual ABJM theory and then discuss recent work on computing 2-loop corrections to world-volume S-matrix in superstring and supermembrane theory.
Posted by: Andrew Svesko
Wed
19 Nov 2025
Extremal Black Holes from Homotopy Algebras
📍 East of England
Chettha Saelim
(University of Surrey)
Abstract:
While strong uniqueness theorems hold for stationary, asymptotically flat black holes in four dimensions, the results break down in higher dimensions and when the asymptotically flat condition is relaxed. Nonetheless, there has been significant progress in classifying the near-horizon geometries of extremal black holes. Motivated by this, we start with near-horizon geometries, which are better understood, and deform them to obtain extremal black hole solutions. We investigate whether a given near-horizon geometry uniquely corresponds to a black hole solution or if there are multiple black holes with the same near-horizon geometry. Our approach employs the homotopy algebraic framework, a powerful and increasingly influential framework in both classical and quantum field theory. Using homological perturbation theory, we recursively solve the deformation problem order by order. To illustrate the method, we present a concrete example of the deformation of the extremal Kerr horizon.
While strong uniqueness theorems hold for stationary, asymptotically flat black holes in four dimensions, the results break down in higher dimensions and when the asymptotically flat condition is relaxed. Nonetheless, there has been significant progress in classifying the near-horizon geometries of extremal black holes. Motivated by this, we start with near-horizon geometries, which are better understood, and deform them to obtain extremal black hole solutions. We investigate whether a given near-horizon geometry uniquely corresponds to a black hole solution or if there are multiple black holes with the same near-horizon geometry. Our approach employs the homotopy algebraic framework, a powerful and increasingly influential framework in both classical and quantum field theory. Using homological perturbation theory, we recursively solve the deformation problem order by order. To illustrate the method, we present a concrete example of the deformation of the extremal Kerr horizon.
Posted by: Julian Kupka
Tue
18 Nov 2025
From Geometry to Scattering Amplitudes
📍 London
Livia Ferro
(University of Hertfordshire)
Abstract:
In recent years it has become clear that particular geometric structures, called positive geometries, underlie various observables in quantum field theories. In this talk I will review this connection for scattering amplitudes. After a broad introduction and review of the main ingredients involved, I will focus on maximally supersymmetric Yang-Mills theory and discuss a positive geometry encoding scattering processes in this theory – the momentum amplituhedron. Finally, I will present some of the main goals and research directions for the future.
In recent years it has become clear that particular geometric structures, called positive geometries, underlie various observables in quantum field theories. In this talk I will review this connection for scattering amplitudes. After a broad introduction and review of the main ingredients involved, I will focus on maximally supersymmetric Yang-Mills theory and discuss a positive geometry encoding scattering processes in this theory – the momentum amplituhedron. Finally, I will present some of the main goals and research directions for the future.
Posted by: Sebastian Cespedes
Tue
18 Nov 2025
Gravitational instantons beyond self-duality
📍 London
Bernardo Araneda
(University of Edinburgh)
Abstract:
Gravitational instantons are four-dimensional, complete, regular and smooth Riemannian manifolds satisfying the Euclidean Einstein equations, which arise naturally in some approaches to quantum gravity. There is a renewed interest in these geometries, thanks to the recent discovery of counterexamples to some famous conjectures, such as Euclidean black hole uniqueness and related problems in Riemannian geometry. After a review of some recent developments focused on the non-hyperkähler case, I will talk about deformations and integrability of the moduli space of ALF instantons.
Gravitational instantons are four-dimensional, complete, regular and smooth Riemannian manifolds satisfying the Euclidean Einstein equations, which arise naturally in some approaches to quantum gravity. There is a renewed interest in these geometries, thanks to the recent discovery of counterexamples to some famous conjectures, such as Euclidean black hole uniqueness and related problems in Riemannian geometry. After a review of some recent developments focused on the non-hyperkähler case, I will talk about deformations and integrability of the moduli space of ALF instantons.
Posted by: João Vilas Boas
Tue
18 Nov 2025
PT-symmetric quantum mechanics: Physics off the real axis
📍 London
Carl Bender
(Washington University)
Abstract:
The average physicist on the street would say that to have a real
energy spectrum and unitary time evolution a quantum Hamiltonian must be Dirac
Hermitian; that is, invariant under complex conjugation + matrix transposition.
However, the non-Dirac-Hermitian Hamiltonian \(H=p^2+ix^3\) has a positive
discrete spectrum and generates unitary time evolution, so \(H\) defines a
consistent physical quantum theory. Thus, Hermiticity symmetry is too
restrictive. While \(H\) is not Dirac Hermitian, it is PT symmetric
(spacetime-reflection symmetric); that is, invariant under parity P + time
reversal T. The quantum mechanics defined by a PT-symmetric Hamiltonian is a
complex generalization of ordinary quantum mechanics. If quantum mechanics
is extended to the complex domain, new theories having remarkable properties
emerge. For example, the Hamiltonian \(H=p^2-x^4\), which has an upside-down
potential, defines two distinct phases, an unstable P-symmetric phase having
complex eigenvalues and a stable PT-symmetric phase whose energy levels are
positive and discrete. The properties of PT-symmetric classical and quantum
systems are under intense study by theorists and experimentalists; many
theoretical predictions have been verified in laboratory experiments.
The average physicist on the street would say that to have a real
energy spectrum and unitary time evolution a quantum Hamiltonian must be Dirac
Hermitian; that is, invariant under complex conjugation + matrix transposition.
However, the non-Dirac-Hermitian Hamiltonian \(H=p^2+ix^3\) has a positive
discrete spectrum and generates unitary time evolution, so \(H\) defines a
consistent physical quantum theory. Thus, Hermiticity symmetry is too
restrictive. While \(H\) is not Dirac Hermitian, it is PT symmetric
(spacetime-reflection symmetric); that is, invariant under parity P + time
reversal T. The quantum mechanics defined by a PT-symmetric Hamiltonian is a
complex generalization of ordinary quantum mechanics. If quantum mechanics
is extended to the complex domain, new theories having remarkable properties
emerge. For example, the Hamiltonian \(H=p^2-x^4\), which has an upside-down
potential, defines two distinct phases, an unstable P-symmetric phase having
complex eigenvalues and a stable PT-symmetric phase whose energy levels are
positive and discrete. The properties of PT-symmetric classical and quantum
systems are under intense study by theorists and experimentalists; many
theoretical predictions have been verified in laboratory experiments.
Posted by: Fedor Levkovich-Maslyuk
Thu
13 Nov 2025
Yangian symmetry, GKZ equations and integrable Feynman graphs
📍 London
Fedor Levkovich-Maslyuk
(City University of 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: Nathan Moynihan
Wed
12 Nov 2025
BMS particles
📍 London
Laura Donnay
(SISSA)
Abstract:
Despite recent progress, a complete formulation of a holographic correspondence for flat spacetimes remains elusive.
Any viable formulation of flat space holography should be based on a correspondence between bulk and boundary states built upon the equivalence of unitary irreducible representations (UIRs) of the asymptotic symmetry group of flat spacetimes, the BMS group. In this talk, I will present explicit wavefunctions for the UIRs of the BMS group (the so-called BMS particles). These are functions on supermomentum space that generalize the familiar notion of Poincaré particles by incorporating additional soft degrees of freedom. I will discuss their connections to infrared physics and outline prospects for defining an S-matrix for BMS states that is free from infrared divergences. This talk is based on joint work with X. Bekaert and Y. Herfray.
Despite recent progress, a complete formulation of a holographic correspondence for flat spacetimes remains elusive.
Any viable formulation of flat space holography should be based on a correspondence between bulk and boundary states built upon the equivalence of unitary irreducible representations (UIRs) of the asymptotic symmetry group of flat spacetimes, the BMS group. In this talk, I will present explicit wavefunctions for the UIRs of the BMS group (the so-called BMS particles). These are functions on supermomentum space that generalize the familiar notion of Poincaré particles by incorporating additional soft degrees of freedom. I will discuss their connections to infrared physics and outline prospects for defining an S-matrix for BMS states that is free from infrared divergences. This talk is based on joint work with X. Bekaert and Y. Herfray.
Posted by: Andrew Svesko
Wed
12 Nov 2025
Localization of strings on group manifolds
📍 London
Sameer Murthy
(Kings College London)
Abstract:
I will discuss how the technique of supersymmetric localization can be adapted to calculate exact bosonic path integrals in a class of theories where the fermions decouple from the bosons. I will then show how this method can be used to calculate the partition function of the WZW model as a sum over classical solutions. I will discuss SU(2) in some detail, as well as two related models: SL(2) and hyperbolic 3-space, i.e. Euclidean AdS3. In all these cases, the exact partition function essentially follows from the knowledge of symmetries and of free fermions.
I will discuss how the technique of supersymmetric localization can be adapted to calculate exact bosonic path integrals in a class of theories where the fermions decouple from the bosons. I will then show how this method can be used to calculate the partition function of the WZW model as a sum over classical solutions. I will discuss SU(2) in some detail, as well as two related models: SL(2) and hyperbolic 3-space, i.e. Euclidean AdS3. In all these cases, the exact partition function essentially follows from the knowledge of symmetries and of free fermions.
Posted by: Jesse van Muiden
Wed
12 Nov 2025
Non-invertible symmetries in non-linear sigma models
📍 East of England
Guillermo Arias Tamargo
(Imperial College London)
Abstract:
Global symmetries can be generalised to transformations generated by topological operators, including cases in which the topological operator does not have an inverse. A family of such topological operators are intimately related to dualities via the procedure of half-space gauging. In this talk I will discuss the construction of non-invertible defects based on T-duality in two dimensions, generalising the well-known case of the free compact boson to any Non-Linear Sigma Model with Wess-Zumino term which is T-dualisable. I will also present several applications of this symmetry, which include the protection of some coupling constants of the sigma model from quantum corrections as well as new Ward identities. Time permitting, I'll discuss the target space interpretation of these defects, and their fate in String Theory.
Global symmetries can be generalised to transformations generated by topological operators, including cases in which the topological operator does not have an inverse. A family of such topological operators are intimately related to dualities via the procedure of half-space gauging. In this talk I will discuss the construction of non-invertible defects based on T-duality in two dimensions, generalising the well-known case of the free compact boson to any Non-Linear Sigma Model with Wess-Zumino term which is T-dualisable. I will also present several applications of this symmetry, which include the protection of some coupling constants of the sigma model from quantum corrections as well as new Ward identities. Time permitting, I'll discuss the target space interpretation of these defects, and their fate in String Theory.
Posted by: Julian Kupka
Tue
11 Nov 2025
de Sitter Universes
📍 London
Alan Rios Fukelman
(QMUL)
Abstract:
In this talk I will discuss features of Quantum Field Theories in a fixed de Sitter background. I will present an exactly solvable model and show how to obtain all loops correlation functions of local operators. I will then discuss the existence of charged vacuum states in the theory and its relation to spontaneous symmetry breaking in de Sitter spacetimes.
In this talk I will discuss features of Quantum Field Theories in a fixed de Sitter background. I will present an exactly solvable model and show how to obtain all loops correlation functions of local operators. I will then discuss the existence of charged vacuum states in the theory and its relation to spontaneous symmetry breaking in de Sitter spacetimes.
Posted by: João Vilas Boas
Tue
11 Nov 2025
Features of the Partition Function of a \(\Lambda>0\) Universe
📍 London
Dionysios Anninos
(KCL)
Abstract:
We discuss properties of the gravitational path integral for rhetorics of gravity with Lambda>0. We consider the problem in various spacetime dimensions, and for various matter fields. Time permitting, we also comment on the two-dimensional case.
We discuss properties of the gravitational path integral for rhetorics of gravity with Lambda>0. We consider the problem in various spacetime dimensions, and for various matter fields. Time permitting, we also comment on the two-dimensional case.
Posted by: Sebastian Cespedes
Mon
10 Nov 2025
Lonti: Introduction to Matrix Models (4/4)
📍 London
Fedor Levkovich-Maslyuk
(City U.)
Abstract:
Models of random matrices can be viewed as zero-dimensional analogs of usual field theory. Despite decades of exploration, matrix models remain at the forefront of intensive research, motivated by a rich web of connections to string theory, quantum gravity, integrability, Yang-Mills theory, combinatorics, geometry and representation theory. These lectures will present a pedagogical introduction to the subject.
Lecture 1. Motivation and basic definitions. Hermitian matrix models: Feynman rules, ribbon graphs, large N genus expansion.
Lecture 2. Reduction to eigenvalues. Large N limit, Coulomb gas approach, saddle point equations.
Lecture 3. Continuum limit of saddle point equations. Eigenvalue density and spectral curve. Examples.
Lecture 4. Orthogonal polynomials. Relation to 2d gravity and phase transitions (sketch). Outlook: loop equations, topological recursion, integrability.
Models of random matrices can be viewed as zero-dimensional analogs of usual field theory. Despite decades of exploration, matrix models remain at the forefront of intensive research, motivated by a rich web of connections to string theory, quantum gravity, integrability, Yang-Mills theory, combinatorics, geometry and representation theory. These lectures will present a pedagogical introduction to the subject.
Lecture 1. Motivation and basic definitions. Hermitian matrix models: Feynman rules, ribbon graphs, large N genus expansion.
Lecture 2. Reduction to eigenvalues. Large N limit, Coulomb gas approach, saddle point equations.
Lecture 3. Continuum limit of saddle point equations. Eigenvalue density and spectral curve. Examples.
Lecture 4. Orthogonal polynomials. Relation to 2d gravity and phase transitions (sketch). Outlook: loop equations, topological recursion, integrability.
Posted by: Damian Galante
Mon
10 Nov 2025
The amplituhedron and cluster structures on scattering amplitudes of the planar N=4 SYM
📍 London
Ran Tessler
(Weizmann)
Abstract:
The amplituhedron is a semi algebraic space introduced in 2013 by Arkani-Hamed and Trnka in their endeavor to understand N=4 Super Yang Mills amplitudes. A surprising property of these amplitudes is that they satisfy mysterious connections with cluster algebras. These connections are both interesting theoretically, and play a crucial role in calculating the amplitudes. In my talk I will describe the amplituhedron, the non-negative Grassmannian on which it is built,. I will then explain one of the central relations with clusters, its proof, and a recent conjectural generalization in the language of operads. Based on joint works with Chaim Even Zohar, Tsviqa Lakrec, Matteo Parisi, Melissa Sherman Bennett and Lauren Williams.
The amplituhedron is a semi algebraic space introduced in 2013 by Arkani-Hamed and Trnka in their endeavor to understand N=4 Super Yang Mills amplitudes. A surprising property of these amplitudes is that they satisfy mysterious connections with cluster algebras. These connections are both interesting theoretically, and play a crucial role in calculating the amplitudes. In my talk I will describe the amplituhedron, the non-negative Grassmannian on which it is built,. I will then explain one of the central relations with clusters, its proof, and a recent conjectural generalization in the language of operads. Based on joint works with Chaim Even Zohar, Tsviqa Lakrec, Matteo Parisi, Melissa Sherman Bennett and Lauren Williams.
Posted by: Evgeny Sobko
Fri
7 Nov 2025
Anomalies of Defect Parameter Spaces and a Spin-Flux Duality
📍 London
Brandon Rayhaun
(IAS Princeton)
Abstract:
I will explain how the irreversibility of the renormalization group together with anomalies, including anomalies in the space of coupling constants, can be used to constrain the IR phases of defects in familiar quantum field theories. As an example, I will use these techniques to provide evidence for a conjectural "spin-flux duality" which describes how certain line operators are mapped across particle/vortex duality in 2+1d.
–-
https://lims.ac.uk/event/anomalies-of-defect-parameter-spaces-and-a-spin-flux-duality/
London Institute for Mathematical Sciences (LIMS),
Royal Institution.
21 Albemarle St,
London W1S 4BS, UK
I will explain how the irreversibility of the renormalization group together with anomalies, including anomalies in the space of coupling constants, can be used to constrain the IR phases of defects in familiar quantum field theories. As an example, I will use these techniques to provide evidence for a conjectural "spin-flux duality" which describes how certain line operators are mapped across particle/vortex duality in 2+1d.
–-
https://lims.ac.uk/event/anomalies-of-defect-parameter-spaces-and-a-spin-flux-duality/
London Institute for Mathematical Sciences (LIMS),
Royal Institution.
21 Albemarle St,
London W1S 4BS, UK
Posted by: JUVEN WANG
Thu
6 Nov 2025
The double copy: new connections in physics and mathematics
📍 London
Chris White
(QMUL)
Abstract:
The matter and fundamental forces in our universe are described by so-called non-abelian gauge theories, and by General Relativity. Traditionally, these theories are very different, but recent research has uncovered a remarkable correspondence - the “double copy” - that precisely relates their mathematical structure. The correspondence relates to other theoretical structures (e.g. string theory), and to an increasingly complex web of exotic field theories. In this talk, I will review the origin of the double copy and its practical applications, before discussing links with open problems in pure mathematics.
The matter and fundamental forces in our universe are described by so-called non-abelian gauge theories, and by General Relativity. Traditionally, these theories are very different, but recent research has uncovered a remarkable correspondence - the “double copy” - that precisely relates their mathematical structure. The correspondence relates to other theoretical structures (e.g. string theory), and to an increasingly complex web of exotic field theories. In this talk, I will review the origin of the double copy and its practical applications, before discussing links with open problems in pure mathematics.
Posted by: Evgeny Sobko
Wed
5 Nov 2025
3d gravity, OPE statistics and the sum over topologies
📍 London
Boris Post
(University of Oxford)
Abstract:
In this talk, I will report some progress in systematizing the correspondence between universal statistical features of 2d CFT data and pure AdS_3 quantum gravity. In particular, I will show that non-handlebodies are necessary in the sum over topologies, in order to furnish a statistical ensemble of OPE data that is compatible with both crossing symmetry and \it{typicality}, a notion familiar from the Eigenstate Thermalization Hypothesis. Using the tools of Virasoro TQFT, I will relate index contractions of random OPE coefficients to surgery operations on 3-manifolds. Combining this surgery with crossing transformations generates a large class of hyperbolic non-handlebodies in the topological expansion of 3d gravity. Based on ongoing work with Alex Belin, Scott Collier, Lorenz Eberhardt and Diego Liska.
In this talk, I will report some progress in systematizing the correspondence between universal statistical features of 2d CFT data and pure AdS_3 quantum gravity. In particular, I will show that non-handlebodies are necessary in the sum over topologies, in order to furnish a statistical ensemble of OPE data that is compatible with both crossing symmetry and \it{typicality}, a notion familiar from the Eigenstate Thermalization Hypothesis. Using the tools of Virasoro TQFT, I will relate index contractions of random OPE coefficients to surgery operations on 3-manifolds. Combining this surgery with crossing transformations generates a large class of hyperbolic non-handlebodies in the topological expansion of 3d gravity. Based on ongoing work with Alex Belin, Scott Collier, Lorenz Eberhardt and Diego Liska.
Posted by: Jesse van Muiden
Wed
5 Nov 2025
Analytic approaches to the relativistic Boltzmann equation
📍 East of England
Ines Aniceto
(University of Southampton)
Abstract:
The emergence of a universal pre-hydrodynamic attractor behaviour during fluid thermalisation is an important feature in the study of ultra-relativistic nuclear collisions and cold atom experiments: highly non-hydrodynamic behaviour dictated by initial conditions quickly decays towards this attractor solution, with the resulting hydrodynamic system independent of the initial state.
There are many approaches to study the emergence of this attractor. We will briefly review these approaches, then focusing on kinetic theory. Starting with the relativist Boltzmann equation in the so-called relaxation time approximation, we introduce a series of moments and their generating function, which we show solved a single PDE. We solve this PDE perturbatively for all moments, both in the small and large time approximations, and we then recover the free streaming and attractor regimes at each end via methods of analytic continuation.
The emergence of a universal pre-hydrodynamic attractor behaviour during fluid thermalisation is an important feature in the study of ultra-relativistic nuclear collisions and cold atom experiments: highly non-hydrodynamic behaviour dictated by initial conditions quickly decays towards this attractor solution, with the resulting hydrodynamic system independent of the initial state.
There are many approaches to study the emergence of this attractor. We will briefly review these approaches, then focusing on kinetic theory. Starting with the relativist Boltzmann equation in the so-called relaxation time approximation, we introduce a series of moments and their generating function, which we show solved a single PDE. We solve this PDE perturbatively for all moments, both in the small and large time approximations, and we then recover the free streaming and attractor regimes at each end via methods of analytic continuation.
Posted by: Julian Kupka
Tue
4 Nov 2025
No-go theorems for higher-spin charges in AdS2
📍 London
António Antunes
(LPENS)
Abstract:
Higher-spin conserved currents and charges feature prominently in integrable 2d QFTs in flat space. Motivated by the question of integrable field theories in curved space and by results of the conformal bootstrap, we will consider the consequences of higher-spin currents for QFTs in AdS2. Namely, we will show that their presence is much more constraining than in flat space in particular proving that it is impossible to preserve: (a) any higher-spin charges when deforming a massive free field by interactions, or (b) any spin-4 charges when deforming a CFT by a Virasoro primary. Along the way, we will show that in AdS one cannot `partially' conserve a higher-spin current and explain how higher-spin charges lead to integer spacing in the spectrum of primaries, and to constraints on correlation functions.
Higher-spin conserved currents and charges feature prominently in integrable 2d QFTs in flat space. Motivated by the question of integrable field theories in curved space and by results of the conformal bootstrap, we will consider the consequences of higher-spin currents for QFTs in AdS2. Namely, we will show that their presence is much more constraining than in flat space in particular proving that it is impossible to preserve: (a) any higher-spin charges when deforming a massive free field by interactions, or (b) any spin-4 charges when deforming a CFT by a Virasoro primary. Along the way, we will show that in AdS one cannot `partially' conserve a higher-spin current and explain how higher-spin charges lead to integer spacing in the spectrum of primaries, and to constraints on correlation functions.
Posted by: João Vilas Boas
Mon
3 Nov 2025
Lonti: Introduction to Matrix Models (3/4)
📍 London
Fedor Levkovich-Maslyuk
(City U.)
Abstract:
Models of random matrices can be viewed as zero-dimensional analogs of usual field theory. Despite decades of exploration, matrix models remain at the forefront of intensive research, motivated by a rich web of connections to string theory, quantum gravity, integrability, Yang-Mills theory, combinatorics, geometry and representation theory. These lectures will present a pedagogical introduction to the subject.
Lecture 1. Motivation and basic definitions. Hermitian matrix models: Feynman rules, ribbon graphs, large N genus expansion.
Lecture 2. Reduction to eigenvalues. Large N limit, Coulomb gas approach, saddle point equations.
Lecture 3. Continuum limit of saddle point equations. Eigenvalue density and spectral curve. Examples.
Models of random matrices can be viewed as zero-dimensional analogs of usual field theory. Despite decades of exploration, matrix models remain at the forefront of intensive research, motivated by a rich web of connections to string theory, quantum gravity, integrability, Yang-Mills theory, combinatorics, geometry and representation theory. These lectures will present a pedagogical introduction to the subject.
Lecture 1. Motivation and basic definitions. Hermitian matrix models: Feynman rules, ribbon graphs, large N genus expansion.
Lecture 2. Reduction to eigenvalues. Large N limit, Coulomb gas approach, saddle point equations.
Lecture 3. Continuum limit of saddle point equations. Eigenvalue density and spectral curve. Examples.
Posted by: Damian Galante
Mon
3 Nov 2025
Black holes, naturalness and the renormalization group
📍 London
Julio Parra-Martinez
(IHES, Paris)
Abstract:
In this talk I will explain how certain aspects of black hole physics can be understood using ideas from effective field theory. Many of the familiar notions from particle physics will play a role, including the renormalization group, universality and naturalness. In particular, I will explain why black holes naively seem like fine-tuned systems, but they are ultimately not. I will also explain how their effective description reveals a degree of universality that can be used to resum certain features of the gravitational waveform for binary mergers observed by LIGO/Virgo/Kagra.
In this talk I will explain how certain aspects of black hole physics can be understood using ideas from effective field theory. Many of the familiar notions from particle physics will play a role, including the renormalization group, universality and naturalness. In particular, I will explain why black holes naively seem like fine-tuned systems, but they are ultimately not. I will also explain how their effective description reveals a degree of universality that can be used to resum certain features of the gravitational waveform for binary mergers observed by LIGO/Virgo/Kagra.
Posted by: Nathan Moynihan
October 2025
Fri
31 Oct 2025
Codimension-2 Super-(Conformal) Monodromy Defects
📍 London
Andrea Conti
(University of Oviedo)
Abstract:
Recently, there has been an increasing interest in the study of defects in quantum field theories, where holography has become a fruitful framework that enables the study of different aspects of super-(conformal) gauge theories.
In this talk, I will discuss supergravity solutions that are dual to super conformal monodromy defects. These solutions are obtained using gauged supergravities in D=4,5,6 and 7 dimensions. I will present a prescription to compute the defect entanglement entropy, outlining the renormalization procedure needed to regularise its divergencies, which I will discuss in detail. In some cases, we are also able to express this quantity in terms of the free energy/Weyl anomaly of the defect and its conformal weight. If time allows, I will also discuss some new results for non-conformal monodromy defects.
Recently, there has been an increasing interest in the study of defects in quantum field theories, where holography has become a fruitful framework that enables the study of different aspects of super-(conformal) gauge theories.
In this talk, I will discuss supergravity solutions that are dual to super conformal monodromy defects. These solutions are obtained using gauged supergravities in D=4,5,6 and 7 dimensions. I will present a prescription to compute the defect entanglement entropy, outlining the renormalization procedure needed to regularise its divergencies, which I will discuss in detail. In some cases, we are also able to express this quantity in terms of the free energy/Weyl anomaly of the defect and its conformal weight. If time allows, I will also discuss some new results for non-conformal monodromy defects.
Posted by: Jesse van Muiden
Thu
30 Oct 2025
Codimension-2 Super-(Conformal) Monodromy Defects
📍 London
Andrea Conti
(University of Oviedo)
Abstract:
Recently, there has been an increasing interest in the study of defects in quantum field theories, where holography has become a fruitful framework that enables the study of different aspects of super-(conformal) gauge theories.
In this talk, I will discuss supergravity solutions that are dual to super conformal monodromy defects. These solutions are obtained using gauged supergravities in D=4,5,6 and 7 dimensions. I will present a prescription to compute the defect entanglement entropy, outlining the renormalization procedure needed to regularise its divergencies, which I will discuss in detail. In some cases, we are also able to express this quantity in terms of the free energy/Weyl anomaly of the defect and its conformal weight. If time allows, I will also discuss some new results for non-conformal monodromy defects.
Recently, there has been an increasing interest in the study of defects in quantum field theories, where holography has become a fruitful framework that enables the study of different aspects of super-(conformal) gauge theories.
In this talk, I will discuss supergravity solutions that are dual to super conformal monodromy defects. These solutions are obtained using gauged supergravities in D=4,5,6 and 7 dimensions. I will present a prescription to compute the defect entanglement entropy, outlining the renormalization procedure needed to regularise its divergencies, which I will discuss in detail. In some cases, we are also able to express this quantity in terms of the free energy/Weyl anomaly of the defect and its conformal weight. If time allows, I will also discuss some new results for non-conformal monodromy defects.
Posted by: Nathan Moynihan
Wed
29 Oct 2025
Color-kinematics duality and double copy theories
📍 London
Maxim Zabzine
(Uppsala University)
Abstract:
I will review the color-kinematics duality for gauge theories in scattering amplitudes and explain
how it manifest itself for the case off-shell duality for Chern-Simons theory. I will discuss the relation to gravity via
double copy constructions. If time allows I will talk about BV formalism behind this construction and some other
examples.
I will review the color-kinematics duality for gauge theories in scattering amplitudes and explain
how it manifest itself for the case off-shell duality for Chern-Simons theory. I will discuss the relation to gravity via
double copy constructions. If time allows I will talk about BV formalism behind this construction and some other
examples.
Posted by: Jesse van Muiden
Wed
29 Oct 2025
Einstein gravity with boundaries
📍 London
Toby Wiseman
(Imperial College London)
Abstract:
We will review some properties of boundaries to spacetime both in a Riemannian and Lorentzian setting for Einstein’s gravity. We will outline some surprising new results about what boundary conditions allow a good behaviour for the bulk theory.
We will review some properties of boundaries to spacetime both in a Riemannian and Lorentzian setting for Einstein’s gravity. We will outline some surprising new results about what boundary conditions allow a good behaviour for the bulk theory.
Posted by: Andrew Svesko
Tue
28 Oct 2025
Encapsulating precession in gravitational wave signal models
📍 London
Eleanor Hamilton
(Universitat de les Illes Balears)
Abstract:
The gravitational wave signal from precessing systems (those where the spins of the black holes are misaligned with the orbital angular momentum of the binary) is complicated by oscillations in the amplitude and phase, making such systems difficult to understand and to model. This is further compounded by a scarcity of highly precessing waveforms available in public catalogues, required for studying the merger-ringdown signal. However, as we venture into an era of increasingly sensitive detectors, it is ever more important to have a thorough understanding of precessing systems– as well as highly accurate, computationally robust models for use in the analysis of gravitational wave signals. I will discuss recent developments and challenges in understanding the phenomenologies of these systems.
The gravitational wave signal from precessing systems (those where the spins of the black holes are misaligned with the orbital angular momentum of the binary) is complicated by oscillations in the amplitude and phase, making such systems difficult to understand and to model. This is further compounded by a scarcity of highly precessing waveforms available in public catalogues, required for studying the merger-ringdown signal. However, as we venture into an era of increasingly sensitive detectors, it is ever more important to have a thorough understanding of precessing systems– as well as highly accurate, computationally robust models for use in the analysis of gravitational wave signals. I will discuss recent developments and challenges in understanding the phenomenologies of these systems.
Posted by: João Vilas Boas
Tue
28 Oct 2025
Cancelled
📍 London
Andre Bernevig
(Princeton University)
Abstract:
Unfortunately this seminar has been cancelled.
Unfortunately this seminar has been cancelled.
Posted by: Sebastian Cespedes
Mon
27 Oct 2025
Lonti: Introduction to Matrix Models (2/4)
📍 London
Fedor Levkovich-Maslyuk
(City U.)
Abstract:
Models of random matrices can be viewed as zero-dimensional analogs of usual field theory. Despite decades of exploration, matrix models remain at the forefront of intensive research, motivated by a rich web of connections to string theory, quantum gravity, integrability, Yang-Mills theory, combinatorics, geometry and representation theory. These lectures will present a pedagogical introduction to the subject.
Lecture 1. Motivation and basic definitions. Hermitian matrix models: Feynman rules, ribbon graphs, large N genus expansion.
Lecture 2. Reduction to eigenvalues. Large N limit, Coulomb gas approach, saddle point equations.
Models of random matrices can be viewed as zero-dimensional analogs of usual field theory. Despite decades of exploration, matrix models remain at the forefront of intensive research, motivated by a rich web of connections to string theory, quantum gravity, integrability, Yang-Mills theory, combinatorics, geometry and representation theory. These lectures will present a pedagogical introduction to the subject.
Lecture 1. Motivation and basic definitions. Hermitian matrix models: Feynman rules, ribbon graphs, large N genus expansion.
Lecture 2. Reduction to eigenvalues. Large N limit, Coulomb gas approach, saddle point equations.
Posted by: Damian Galante
Fri
24 Oct 2025
Charge Quantisation, Monopoles and Instantons in the Standard Model
📍 London
Valya Khoze
(IPPP Durham University)
Wed
22 Oct 2025
Weak Parity Violation, Strong CP Problem, and Symmetric Mass Generation
📍 East of England
Juven Wang
(London Institute for Mathematical Sciences; Harvard University)
Abstract:
See https://www.newton.ac.uk/seminar/49000/
Date 22 October 2025 – 13:15 to 14:45
Venue INI Seminar Room 2
Weak Parity Violation means that the the weak force in the Standard Model exhibits maximal parity violation, coupling exclusively to left-handed fermions. In contrast, the Strong CP Problem asks why strong force appears to preserve CP symmetry so precisely—namely, why the effective QCD θ-angle is zero or extremely small. In this talk, I will discuss how these two long-standing puzzles in the weak and strong sectors may be intimately connected and resolved through Symmetric Mass Generation (SMG) — a novel mechanism by which matters acquire mass without spontaneous symmetry breaking, within an anomaly-free symmetry framework. I will illustrate the idea using a set of toy models, possibly formulated in dimensions other than 4, that capture the essential features of this proposed resolution. References therein: arXiv 2204.14271, 2207.14813, 2212.14036.
See https://www.newton.ac.uk/seminar/49000/
Date 22 October 2025 – 13:15 to 14:45
Venue INI Seminar Room 2
Weak Parity Violation means that the the weak force in the Standard Model exhibits maximal parity violation, coupling exclusively to left-handed fermions. In contrast, the Strong CP Problem asks why strong force appears to preserve CP symmetry so precisely—namely, why the effective QCD θ-angle is zero or extremely small. In this talk, I will discuss how these two long-standing puzzles in the weak and strong sectors may be intimately connected and resolved through Symmetric Mass Generation (SMG) — a novel mechanism by which matters acquire mass without spontaneous symmetry breaking, within an anomaly-free symmetry framework. I will illustrate the idea using a set of toy models, possibly formulated in dimensions other than 4, that capture the essential features of this proposed resolution. References therein: arXiv 2204.14271, 2207.14813, 2212.14036.
Posted by: JUVEN WANG
Wed
22 Oct 2025
Higher Berry phase and multi wavefunction overlap in (2+1) dimensions
📍 London
Shinshei Ryu
(Princeton University)
Abstract:
The Berry phase has played a central role in our understanding of quantum phases of matter. While the conventional Berry phase is given in terms of 1-form connection (Berry connection), recent developments point toward a natural generalization – higher Berry phases – involving connections of higher degree forms. Progress along this direction has been made through tensor-network formulations, revealing connections between higher Berry phases and string field theory. In this talk, I will discuss how higher Berry phases for (2+1)-dimensional gapped quantum states can be formulated and computed using tensor-network methods and conformal field theory.
The Berry phase has played a central role in our understanding of quantum phases of matter. While the conventional Berry phase is given in terms of 1-form connection (Berry connection), recent developments point toward a natural generalization – higher Berry phases – involving connections of higher degree forms. Progress along this direction has been made through tensor-network formulations, revealing connections between higher Berry phases and string field theory. In this talk, I will discuss how higher Berry phases for (2+1)-dimensional gapped quantum states can be formulated and computed using tensor-network methods and conformal field theory.
Posted by: Jesse van Muiden
Wed
22 Oct 2025
Hyperbolic Mass in 2+1 Dimensions
📍 London
Raphaela Wutte
(University of Southampton)
Abstract:
Solutions to general relativity with a negative cosmological constant have received significant attention due to the conjectured AdS/CFT correspondence, a particularly well-understood example of which is exhibited in 2+1 dimensions. I will review known vacuum solutions to general relativity with a negative cosmological constant in 2+1 dimensions and discuss the difficulties in defining mass, which are resolved via minimisation using a positive energy theorem. I will present a gluing theorem for vacuum time-symmetric general-relativistic initial data sets in two spatial dimensions. By gluing two given time-symmetric vacuum initial data sets at conformal infinity, we obtain new time-symmetric vacuum initial data sets. I will sketch the derivation of the mass formulae of the resulting manifolds. Our gluing theorem yields complete manifolds with any mass aspect function, which are smooth except for one conical singularity.
Solutions to general relativity with a negative cosmological constant have received significant attention due to the conjectured AdS/CFT correspondence, a particularly well-understood example of which is exhibited in 2+1 dimensions. I will review known vacuum solutions to general relativity with a negative cosmological constant in 2+1 dimensions and discuss the difficulties in defining mass, which are resolved via minimisation using a positive energy theorem. I will present a gluing theorem for vacuum time-symmetric general-relativistic initial data sets in two spatial dimensions. By gluing two given time-symmetric vacuum initial data sets at conformal infinity, we obtain new time-symmetric vacuum initial data sets. I will sketch the derivation of the mass formulae of the resulting manifolds. Our gluing theorem yields complete manifolds with any mass aspect function, which are smooth except for one conical singularity.
Posted by: Andrew Svesko
Tue
21 Oct 2025
Imaging black holes at high frequency
📍 London
Joydeep Chakravarty
(McGill University)
Abstract:
We devise a formalism to probe local physics about a bulk point in general geometries using boundary correlators. In the exterior region, this allows for the factorization of boundary correlators in terms of flat-space like scattering amplitudes. The formalism also leads to direct measurements using lightcones emerging from the bulk point, capturing the boundary imprint of bulk causality.
Next, we use it to understand the physics of the black hole interior using the past lightcone, where we generalize known relations involving two-point correlators to spectral density tails and to four-point correlators. Details about the interior tunnel to the exterior at the cost of a Boltzmann suppression exp(-1/(2Tx)), where x is the desired spatial resolution. We comment on the relation (or lack thereof) between such measurements and the experience of infalling observers.
We devise a formalism to probe local physics about a bulk point in general geometries using boundary correlators. In the exterior region, this allows for the factorization of boundary correlators in terms of flat-space like scattering amplitudes. The formalism also leads to direct measurements using lightcones emerging from the bulk point, capturing the boundary imprint of bulk causality.
Next, we use it to understand the physics of the black hole interior using the past lightcone, where we generalize known relations involving two-point correlators to spectral density tails and to four-point correlators. Details about the interior tunnel to the exterior at the cost of a Boltzmann suppression exp(-1/(2Tx)), where x is the desired spatial resolution. We comment on the relation (or lack thereof) between such measurements and the experience of infalling observers.
Posted by: João Vilas Boas
Tue
21 Oct 2025
Gravity in the era of Stage IV Surveys
📍 London
Alessandra Silvestri
(Leiden University)
Abstract:
Stage IV Large Scale Structure Surveys are ushering in a new
era of precision cosmology! In this talk, I will explore the effort to test gravity on cosmological
scales, highlighting the theoretical advancements aimed at constructing
an optimal framework. I will also touch on the synergy with
gravitational wave surveys. Additionally, I will provide a detailed
review of recent findings based on currently available data and conclude
with an outlook on the challenges and future prospects in this field.
Stage IV Large Scale Structure Surveys are ushering in a new
era of precision cosmology! In this talk, I will explore the effort to test gravity on cosmological
scales, highlighting the theoretical advancements aimed at constructing
an optimal framework. I will also touch on the synergy with
gravitational wave surveys. Additionally, I will provide a detailed
review of recent findings based on currently available data and conclude
with an outlook on the challenges and future prospects in this field.
Posted by: Sebastian Cespedes
Mon
20 Oct 2025
Lonti: Introduction to Matrix Models (1/4)
📍 London
Fedor Levkovich-Maslyuk
(City U.)
Abstract:
Models of random matrices can be viewed as zero-dimensional analogs of usual field theory. Despite decades of exploration, matrix models remain at the forefront of intensive research, motivated by a rich web of connections to string theory, quantum gravity, integrability, Yang-Mills theory, combinatorics, geometry and representation theory. These lectures will present a pedagogical introduction to the subject.
Lecture 1. Motivation and basic definitions. Hermitian matrix models: Feynman rules, ribbon graphs, large N genus expansion.
Models of random matrices can be viewed as zero-dimensional analogs of usual field theory. Despite decades of exploration, matrix models remain at the forefront of intensive research, motivated by a rich web of connections to string theory, quantum gravity, integrability, Yang-Mills theory, combinatorics, geometry and representation theory. These lectures will present a pedagogical introduction to the subject.
Lecture 1. Motivation and basic definitions. Hermitian matrix models: Feynman rules, ribbon graphs, large N genus expansion.
Posted by: Damian Galante
Fri
17 Oct 2025
Phases of 2d Gauge Theories and Symmetric Mass Generation
📍 London
Rishi Mouland
(Imperial ICL)
Abstract:
We study the dynamics and phase structure of Abelian gauge theories in d=1+1 dimensions. These include U(1) gauge theory coupled to a scalar and a fermion, as well as the two-flavour Schwinger model with different charges. Both theories exhibit a surprisingly rich phase diagram as masses are varied, with both c=1 and c=1/2 critical lines or points. We build up to the study of 2d chiral gauge theories, which hold particular interest because they provide a mechanism for symmetric mass generation, a phenomenon in which fermions become gapped without breaking chiral symmetries.
We study the dynamics and phase structure of Abelian gauge theories in d=1+1 dimensions. These include U(1) gauge theory coupled to a scalar and a fermion, as well as the two-flavour Schwinger model with different charges. Both theories exhibit a surprisingly rich phase diagram as masses are varied, with both c=1 and c=1/2 critical lines or points. We build up to the study of 2d chiral gauge theories, which hold particular interest because they provide a mechanism for symmetric mass generation, a phenomenon in which fermions become gapped without breaking chiral symmetries.
Posted by: JUVEN WANG
Fri
17 Oct 2025
Grothendieck & ’t Hooft: Dessins d’Enfant from AdS/CFT
📍 London
Edward Mazenc
(ETH, Zurich)
Abstract:
In the later part of his life, Grothendieck became fascinated by the fact that certain simple graphs can encode holomorphic maps to the sphere. He called them dessins d’enfants — “children’s drawings.”
Meanwhile, over fifty years ago, ’t Hooft observed that the 1/N expansion in gauge theory closely mirrors the genus expansion in string theory, suggesting a relation between Feynman diagrams and string worldsheets.
I will discuss how recent efforts to derive the AdS/CFT correspondence unite these two perspectives: Grothendieck’s surprise emerges as the simplest instance of gauge/string duality.
In the later part of his life, Grothendieck became fascinated by the fact that certain simple graphs can encode holomorphic maps to the sphere. He called them dessins d’enfants — “children’s drawings.”
Meanwhile, over fifty years ago, ’t Hooft observed that the 1/N expansion in gauge theory closely mirrors the genus expansion in string theory, suggesting a relation between Feynman diagrams and string worldsheets.
I will discuss how recent efforts to derive the AdS/CFT correspondence unite these two perspectives: Grothendieck’s surprise emerges as the simplest instance of gauge/string duality.
Posted by: Yang-Hui He
Thu
16 Oct 2025
Symmetry constraints on defects and scattering amplitudes
📍 London
Christian Copetti
(Oxford University)
Abstract:
Symmetry is a powerful organizing principle, allowing for all-order predictions about the behaviour of quantum systems. In this talk I explain how (generalized) symmetries act on boundary conditions and defects, and use these ideas to constrain fundamental properties of (1+1)d scattering amplitudes, such as crossing symmetry, and screening of UV defects by bulk degrees of freedom.
Symmetry is a powerful organizing principle, allowing for all-order predictions about the behaviour of quantum systems. In this talk I explain how (generalized) symmetries act on boundary conditions and defects, and use these ideas to constrain fundamental properties of (1+1)d scattering amplitudes, such as crossing symmetry, and screening of UV defects by bulk degrees of freedom.
Posted by: Evgeny Sobko
Thu
16 Oct 2025
Gravity from Entropy
📍 London
Ginestra Bianconi
(QMUL)
Abstract:
Gravity is derived from an entropic action coupling matter fields with geometry called Gravity from Entropy action [1]. The fundamental idea is to relate the metric of Lorentzian spacetime to a quantum operator, playing the role of a renormalizable effective density matrix and to describe the matter fields topologically, according to a Dirac-Kähler formalism, as the direct sum of a 0-form, a 1-form and a 2-form. While the geometry of spacetime is defined by its metric, the matter fields can be used to define an alternative metric, the metric induced by the matter fields and curvature. The proposed Gravity from Entropy (GfE) action is associated to a Lagrangian given by a novel geometric quantum relative entropy (GQRE) between the metric of spacetime and the metric induced by the matter fields and curvature which capture the entanglement between geometric degrees of freedom of spacetime. The modified Einstein equations obtained from this action reduce to the Einstein equations with zero cosmological constant in the regime of low coupling. By introducing the G-field, which acts as a set of Lagrangian multipliers, and interpreting it a physical and measurable field, the proposed entropic action reduces to a dressed Einstein-Hilbert action with an emergent positive cosmological constant only dependent on the G-field. The obtained equations of modified gravity remain second order in the metric and in the G-field. Interestingly the GfE action when calculated on Schwarzschild metric allows us to derive from first principles the area law for black holes with large Schwarzschild radius [2]. A canonical quantization of this field theory could bring new insights into quantum gravity while further research might clarify the role that the G-field could have for dark matter.
[1] Bianconi, G., 2025. Gravity from entropy. Physical Review D, 111(6), p.066001.
[2] Bianconi, G., 2025. The quantum relative entropy of the Schwarzschild black hole and the area law. Entropy, 27(3), p.266.
Gravity is derived from an entropic action coupling matter fields with geometry called Gravity from Entropy action [1]. The fundamental idea is to relate the metric of Lorentzian spacetime to a quantum operator, playing the role of a renormalizable effective density matrix and to describe the matter fields topologically, according to a Dirac-Kähler formalism, as the direct sum of a 0-form, a 1-form and a 2-form. While the geometry of spacetime is defined by its metric, the matter fields can be used to define an alternative metric, the metric induced by the matter fields and curvature. The proposed Gravity from Entropy (GfE) action is associated to a Lagrangian given by a novel geometric quantum relative entropy (GQRE) between the metric of spacetime and the metric induced by the matter fields and curvature which capture the entanglement between geometric degrees of freedom of spacetime. The modified Einstein equations obtained from this action reduce to the Einstein equations with zero cosmological constant in the regime of low coupling. By introducing the G-field, which acts as a set of Lagrangian multipliers, and interpreting it a physical and measurable field, the proposed entropic action reduces to a dressed Einstein-Hilbert action with an emergent positive cosmological constant only dependent on the G-field. The obtained equations of modified gravity remain second order in the metric and in the G-field. Interestingly the GfE action when calculated on Schwarzschild metric allows us to derive from first principles the area law for black holes with large Schwarzschild radius [2]. A canonical quantization of this field theory could bring new insights into quantum gravity while further research might clarify the role that the G-field could have for dark matter.
[1] Bianconi, G., 2025. Gravity from entropy. Physical Review D, 111(6), p.066001.
[2] Bianconi, G., 2025. The quantum relative entropy of the Schwarzschild black hole and the area law. Entropy, 27(3), p.266.
Posted by: Nathan Moynihan
Wed
15 Oct 2025
Towards quantum computing strongly-interacting systems with quantum link gauge theories
📍 London
Debasish Banerjee
(University of Southampton)
Abstract:
The development in quantum technologies is matched by an equal energetic activity in formulations of quantum field theories, especially as quantum many-body Hamiltonians, suitable for implementation in quantum simulation and computers. In this talk, we discuss the quantum link formulation of lattice gauge theories, which has not only enabled successful synergy between particle and condensed matter physics, but have also pointed towards the existence of quantum scars which violate the eigenstate thermalization hypothesis and resist thermalization under unitary dynamics. Abelian quantum link models have also been implemented in quantum simulators and computers.
The development in quantum technologies is matched by an equal energetic activity in formulations of quantum field theories, especially as quantum many-body Hamiltonians, suitable for implementation in quantum simulation and computers. In this talk, we discuss the quantum link formulation of lattice gauge theories, which has not only enabled successful synergy between particle and condensed matter physics, but have also pointed towards the existence of quantum scars which violate the eigenstate thermalization hypothesis and resist thermalization under unitary dynamics. Abelian quantum link models have also been implemented in quantum simulators and computers.
Posted by: João Vilas Boas
Wed
15 Oct 2025
Supercurrents and (partial) supersymmetry in 2d adjoint QCD and its generalizations
📍 London
Silviu Pufu
(Princeton University)
Abstract:
The 1+1-dimensional adjoint QCD theory (namely SU(N) gauge theory coupled to a Majorana fermion in the adjoint representation of the gauge group) has the curious property that at a certain non-zero ratio of the fermion mass to the gauge coupling, it exhibits (1, 1) supersymmetry. I will shed some new light onto the supersymmetry of 2d adjoint QCD using several analytical and numerical methods, including the construction of a gauge-invariant, Lorentz-covariant supercurrent, whose conservation relies on the presence of a quantum anomaly. Lastly, I will discuss generalizations of the adjoint QCD theory that exhibit supersymmetric sectors.
The 1+1-dimensional adjoint QCD theory (namely SU(N) gauge theory coupled to a Majorana fermion in the adjoint representation of the gauge group) has the curious property that at a certain non-zero ratio of the fermion mass to the gauge coupling, it exhibits (1, 1) supersymmetry. I will shed some new light onto the supersymmetry of 2d adjoint QCD using several analytical and numerical methods, including the construction of a gauge-invariant, Lorentz-covariant supercurrent, whose conservation relies on the presence of a quantum anomaly. Lastly, I will discuss generalizations of the adjoint QCD theory that exhibit supersymmetric sectors.
Posted by: Charles Thull
Wed
15 Oct 2025
Precision holography for Dp-branes
📍 London
Nikolay Bobev
(KU Leuven)
Abstract:
I will discuss precision holography for the non-conformal SYM theories arising on the worldvolume of coincident Dp-branes. I will show how the free energy of the planar SYM theory on the round sphere and the expectation values of fundamental BPS Wilson loops can be computed explicitly by utilizing supersymmetric localization. I will then present a class of supergravity backgrounds that capture the backreaction of spherical Dp-branes and provide a holographic description of the SYM theory. I will show that the supergravity calculations of the free energy and the Wilson loop expectation value are in precise agreement with the supersymmetric localization results. Finally, I will exploit the scaling similarity property of the Dp-brane supergravity solutions to derive simple Witten diagram rules for the calculation of n-point correlation functions and will show how to explicitly compute 2pt- and 3pt-functions. This leads to explicit results of the 2pt- and 3pt-functions of scalar BPS operators in the planar strongly-coupled SYM theory, including the cases of the BFSS model and the 3d maximally supersymmetric YM theory, that could be tested using lattice QFT methods.
I will discuss precision holography for the non-conformal SYM theories arising on the worldvolume of coincident Dp-branes. I will show how the free energy of the planar SYM theory on the round sphere and the expectation values of fundamental BPS Wilson loops can be computed explicitly by utilizing supersymmetric localization. I will then present a class of supergravity backgrounds that capture the backreaction of spherical Dp-branes and provide a holographic description of the SYM theory. I will show that the supergravity calculations of the free energy and the Wilson loop expectation value are in precise agreement with the supersymmetric localization results. Finally, I will exploit the scaling similarity property of the Dp-brane supergravity solutions to derive simple Witten diagram rules for the calculation of n-point correlation functions and will show how to explicitly compute 2pt- and 3pt-functions. This leads to explicit results of the 2pt- and 3pt-functions of scalar BPS operators in the planar strongly-coupled SYM theory, including the cases of the BFSS model and the 3d maximally supersymmetric YM theory, that could be tested using lattice QFT methods.
Posted by: Charles Thull
Tue
14 Oct 2025
Neural Networks for Theoretical Calculations
📍 London
Daniel Maitre
(Durham)
Abstract:
Machine learning is transforming the way many many aspect of particle physics research is pursued. In this talk I will show a few different ways in which neural networks can be leveraged to make theoretical calculations more efficient and allow it to leverage the newest hardware and software developments.
Machine learning is transforming the way many many aspect of particle physics research is pursued. In this talk I will show a few different ways in which neural networks can be leveraged to make theoretical calculations more efficient and allow it to leverage the newest hardware and software developments.
Posted by: Sebastian Cespedes
Thu
9 Oct 2025
A fresh look at the Froissart bound
📍 London
Andrea Guerrieri
(City University of London)
Abstract:
The Froissart bound is the most celebrated result of the "analytic S-matrix" program.
It sets an absolute upper limit on total cross-sections at asymptotically high energies in any relativistic quantum theory. In this talk I will discuss an alternative version of this problem and derive rigorous bounds on the cross-section at finite energy, combining analytic techniques and non-perturbative S-matrix bootstrap. I will then discuss the amplitude that saturates our bounds, highlighting its distinctive and rather peculiar properties and connecting them with ancient expectations physicists had on non-perturbative growing amplitudes.
The Froissart bound is the most celebrated result of the "analytic S-matrix" program.
It sets an absolute upper limit on total cross-sections at asymptotically high energies in any relativistic quantum theory. In this talk I will discuss an alternative version of this problem and derive rigorous bounds on the cross-section at finite energy, combining analytic techniques and non-perturbative S-matrix bootstrap. I will then discuss the amplitude that saturates our bounds, highlighting its distinctive and rather peculiar properties and connecting them with ancient expectations physicists had on non-perturbative growing amplitudes.
Posted by: Nathan Moynihan
Wed
8 Oct 2025
An integrable sector for the membrane
📍 London
David Osten
(U. Wroclaw)
Abstract:
In contrast to string sigma models which are well-known to be (classically) integrable in certain backgrounds, most famously flat space or AdS(5) x S(5), the same is not true for the membrane sigma model. Reasons for this are the non-trivial gravity on the world-volume but also the rarity of three-dimensional integrable field theories in general. Here, I will present the novel observation that a certain decoupling limit of the membrane in certain backgrounds will lead to an integrable model, the Manakov-Zakharov-Ward model – a known three-dimensional, but non-relativistic, integrable field theory. As an example of a supergravity background in which this limit is possible is the 11d uplift of the pure NS-NS AdS(3) x S(3) x T(4) background.
In contrast to string sigma models which are well-known to be (classically) integrable in certain backgrounds, most famously flat space or AdS(5) x S(5), the same is not true for the membrane sigma model. Reasons for this are the non-trivial gravity on the world-volume but also the rarity of three-dimensional integrable field theories in general. Here, I will present the novel observation that a certain decoupling limit of the membrane in certain backgrounds will lead to an integrable model, the Manakov-Zakharov-Ward model – a known three-dimensional, but non-relativistic, integrable field theory. As an example of a supergravity background in which this limit is possible is the 11d uplift of the pure NS-NS AdS(3) x S(3) x T(4) background.
Posted by: Jesse van Muiden
Tue
7 Oct 2025
[Postponed to 18 November] Resurgent symmetry of quantum mirror curves
📍 South East
Claudia Rella
(IHES)
Abstract:
This seminar will now take place on 18 November
This seminar will now take place on 18 November
Posted by: Ömer Gürdoğan
Tue
7 Oct 2025
Sharp Transitions for Subsystem Complexity
📍 London
Andreas Karch
(University of Texas)
Abstract:
The circuit complexity of time-evolved pure quantum states
grows linearly in time for an exponentially long time. This behavior has
been proven in certain models, is conjectured to hold for generic
quantum many-body systems, and is believed to be dual to the long-time
growth of black hole interiors in AdS/CFT. Achieving a similar
understanding for mixed states remains an important problem. We
demonstrate that holography predicts several sharp transitions in the
time evolution of subsystem complexity and show that at least some of
these transitions are also realized in random quantum circuits.
The circuit complexity of time-evolved pure quantum states
grows linearly in time for an exponentially long time. This behavior has
been proven in certain models, is conjectured to hold for generic
quantum many-body systems, and is believed to be dual to the long-time
growth of black hole interiors in AdS/CFT. Achieving a similar
understanding for mixed states remains an important problem. We
demonstrate that holography predicts several sharp transitions in the
time evolution of subsystem complexity and show that at least some of
these transitions are also realized in random quantum circuits.
Posted by: Sebastian Cespedes
Fri
3 Oct 2025
Wall-crossing and scattering diagrams in geometry and beyond.
📍 London
Mark Gross
(Cambridge)
Abstract:
I will discuss the notion of scattering diagrams, which encode often very complex data of wall-crossing for various kinds of geometric problems. These originally originated in work of Kontsevich-Soibelman, but have been found to occur naturally in many different contexts, from mirror symmetry, cluster algebras, wall-crossing for moduli spaces of sheaves, and theoretical physics.
I will discuss the notion of scattering diagrams, which encode often very complex data of wall-crossing for various kinds of geometric problems. These originally originated in work of Kontsevich-Soibelman, but have been found to occur naturally in many different contexts, from mirror symmetry, cluster algebras, wall-crossing for moduli spaces of sheaves, and theoretical physics.
Posted by: Yang-Hui He
Fri
3 Oct 2025
Integrable models, spin and statistics
📍 London
Alessandro Torrielli
(University of Surrey)
Abstract:
Integrable models in 1+1 dimensions allows for exact solutions of their scattering problems, and often a complete derivation of the spectrum by means of algebraic methods. However, we rarely stop and wonder what the particles which we are scattering really are. In such low dimensionality, bosons, fermions, spin and statistics are actually far stranger than in our 3+1 dimensional world, and interesting phenomena are possible. We will discuss some generalities about spin and statistics in 1+1 dimensions, and then delve into one manifestation of this strange behaviour in AdS_3 string theory.
Integrable models in 1+1 dimensions allows for exact solutions of their scattering problems, and often a complete derivation of the spectrum by means of algebraic methods. However, we rarely stop and wonder what the particles which we are scattering really are. In such low dimensionality, bosons, fermions, spin and statistics are actually far stranger than in our 3+1 dimensional world, and interesting phenomena are possible. We will discuss some generalities about spin and statistics in 1+1 dimensions, and then delve into one manifestation of this strange behaviour in AdS_3 string theory.
Posted by: Evgeny Sobko
Wed
1 Oct 2025
Integrability without Elastic Scattering
📍 London
Sibylle Driezen
(ETH)
Abstract:
Integrability provides a rare tool for accessing strongly coupled quantum field theories. To extend our understanding, it is important to study cases where the integrable structure departs significantly from known examples. I will discuss recent work on Drinfel’d twists of the Jordanian type in the spin chain formulation of the AdS_5 x S^5 superstring, which can be interpreted as spin chain avatars of worldsheet non-abelian T-duality. On the string side these deformations are Lax integrable, yet they lead to particle production, raising sharp questions about the scope and fate of integrability studies based on factorised and elastic S-matrices. From the spin-chain perspective, however, a different picture emerges: the natural eigenstates are organised not by particle number but by a residual non-Cartan symmetry. In this basis the spectrum follows from a simple Baxter equation, which we show to agree with (semi-)classical string energies computed from the algebraic curve. This provides not only the first evidence for a non-abelian deformed AdS/CFT duality (which is relevant for non-AdS holography), but also highlights a broader lesson: particle production need not signal the end of integrability, but may instead point to new forms in which it survives.
Integrability provides a rare tool for accessing strongly coupled quantum field theories. To extend our understanding, it is important to study cases where the integrable structure departs significantly from known examples. I will discuss recent work on Drinfel’d twists of the Jordanian type in the spin chain formulation of the AdS_5 x S^5 superstring, which can be interpreted as spin chain avatars of worldsheet non-abelian T-duality. On the string side these deformations are Lax integrable, yet they lead to particle production, raising sharp questions about the scope and fate of integrability studies based on factorised and elastic S-matrices. From the spin-chain perspective, however, a different picture emerges: the natural eigenstates are organised not by particle number but by a residual non-Cartan symmetry. In this basis the spectrum follows from a simple Baxter equation, which we show to agree with (semi-)classical string energies computed from the algebraic curve. This provides not only the first evidence for a non-abelian deformed AdS/CFT duality (which is relevant for non-AdS holography), but also highlights a broader lesson: particle production need not signal the end of integrability, but may instead point to new forms in which it survives.
Posted by: Jesse van Muiden
Wed
1 Oct 2025
Quantum Gravity in Near-Extremal Black Holes
📍 London
Roberto Emparan
(University of Barcelona)
Abstract:
Recent developments have revealed that black holes near extremality exhibit large quantum fluctuations in their geometry, marking a controllable breakdown of semiclassical quantum field theory in curved spacetime. In this talk, I will discuss how these fluctuations can be revealed through scattering waves off the black hole. In particular, we find that extremely cold black holes become transparent to low-frequency light or gravitational radiation. These effects provide concrete signatures of quantum gravity at play in near-extremal regimes.
Recent developments have revealed that black holes near extremality exhibit large quantum fluctuations in their geometry, marking a controllable breakdown of semiclassical quantum field theory in curved spacetime. In this talk, I will discuss how these fluctuations can be revealed through scattering waves off the black hole. In particular, we find that extremely cold black holes become transparent to low-frequency light or gravitational radiation. These effects provide concrete signatures of quantum gravity at play in near-extremal regimes.
Posted by: Andrew Svesko
September 2025
Tue
30 Sep 2025
Negative Energy
📍 London
Stefan Hollands
(Leipzig University)
Abstract:
Ordinarily, the actual energy is not physically significant but only energy differences are. But in general relativity, the absolute energy (density) appears on the right side of the Einstein equations as a component of the stress tensor. In this colloquium I explore how negative energy densities are thereby related to exotic phenomena such as warp drive spacetimes or wormholes. Quantum fluctuations enable negative energies and can be tiny, e.g. in the halos of black holes, or astronomical, e.g. inside black holes. In many interesting cases, the laws of physics limit the amount of possible negative energy, and such laws can be seen as a fundamental bridge between gravity and quantum information..
Ordinarily, the actual energy is not physically significant but only energy differences are. But in general relativity, the absolute energy (density) appears on the right side of the Einstein equations as a component of the stress tensor. In this colloquium I explore how negative energy densities are thereby related to exotic phenomena such as warp drive spacetimes or wormholes. Quantum fluctuations enable negative energies and can be tiny, e.g. in the halos of black holes, or astronomical, e.g. inside black holes. In many interesting cases, the laws of physics limit the amount of possible negative energy, and such laws can be seen as a fundamental bridge between gravity and quantum information..
Posted by: Sebastian Cespedes
Thu
25 Sep 2025
Gravity from entropy
📍 London
Ginestra Bianconi
(QML)
Abstract:
Gravity is derived from an action given by the geometrical quantum relative entropy coupling matter fields with geometry. The fundamental idea is to relate the metric of Lorentzian spacetime to a quantum operator, playing the role of an renormalizable effective density matrix and to describe the matter fields topologically, according to a Dirac-Kähler formalism, as the direct sum of a 0-form, a 1-form and a 2-form. While the geometry of spacetime is defined by its metric, the matter fields can be used to define an alternative metric, the metric induced by the matter fields, which geometrically describes the interplay between spacetime and matter. The proposed entropic action is the geometric quantum relative entropy between the metric of spacetime and the metric induced by the matter fields. The modified Einstein equations obtained from this action reduce to the Einstein equations with zero cosmological constant in the regime of low coupling. By introducing the G-field, which acts as a set of Lagrangian multipliers, the proposed entropic action reduces to a dressed Einstein-Hilbert action with an emergent small and positive cosmological constant only dependent on the G-field. The obtained equations of modified gravity remain second order in the metric and in the G-field. A canonical quantization of this field theory could bring new insights into quantum gravity while further research might clarify the role that the G-field could have for dark matter.
We furthermore show that the geometrical quantum relative entropy associated to the Schwarzschild metric, which provides an approximate solution of the modified gravity equations, follows the area law for large Schwarzschild radius.
Bianconi, G., 2025. Gravity from entropy. Physical Review D, 111(6), p.066001.
Bianconi, G., 2025. The quantum relative entropy of the Schwarzschild black hole and the area law. Entropy, 27(3), p.266.
Gravity is derived from an action given by the geometrical quantum relative entropy coupling matter fields with geometry. The fundamental idea is to relate the metric of Lorentzian spacetime to a quantum operator, playing the role of an renormalizable effective density matrix and to describe the matter fields topologically, according to a Dirac-Kähler formalism, as the direct sum of a 0-form, a 1-form and a 2-form. While the geometry of spacetime is defined by its metric, the matter fields can be used to define an alternative metric, the metric induced by the matter fields, which geometrically describes the interplay between spacetime and matter. The proposed entropic action is the geometric quantum relative entropy between the metric of spacetime and the metric induced by the matter fields. The modified Einstein equations obtained from this action reduce to the Einstein equations with zero cosmological constant in the regime of low coupling. By introducing the G-field, which acts as a set of Lagrangian multipliers, the proposed entropic action reduces to a dressed Einstein-Hilbert action with an emergent small and positive cosmological constant only dependent on the G-field. The obtained equations of modified gravity remain second order in the metric and in the G-field. A canonical quantization of this field theory could bring new insights into quantum gravity while further research might clarify the role that the G-field could have for dark matter.
We furthermore show that the geometrical quantum relative entropy associated to the Schwarzschild metric, which provides an approximate solution of the modified gravity equations, follows the area law for large Schwarzschild radius.
Bianconi, G., 2025. Gravity from entropy. Physical Review D, 111(6), p.066001.
Bianconi, G., 2025. The quantum relative entropy of the Schwarzschild black hole and the area law. Entropy, 27(3), p.266.
Posted by: Yang-Hui He
Thu
25 Sep 2025
Trans-IR flows and BKL dynamics in AdS black holes
📍 London
Ayan Kumar Patra
Abstract:
The interior of asymptotically AdS black holes provides a setting where one can naturally extend the notion of holographic RG flows past their conventional infrared fixed points. In this talk, I will describe how these extended “trans-IR” flows provide a unique framework for capturing gravitational dynamics behind the horizon, especially as one approaches a spacelike singularity. Near the singularity, the geometry enters a regime governed by the BKL conjecture and characterized by a sequence of Kasner epochs and eras. To get a handle on the degrees of freedom involved in this evolution, I will introduce a monotonic function, known as the thermal a-function, which tracks the flow into the trans-IR region. With this function, I will show that the full sequence of Kasner epochs and eras can be effectively captured, and the degrees of freedom thin out and ultimately vanish at the trans-IR fixed point.
The interior of asymptotically AdS black holes provides a setting where one can naturally extend the notion of holographic RG flows past their conventional infrared fixed points. In this talk, I will describe how these extended “trans-IR” flows provide a unique framework for capturing gravitational dynamics behind the horizon, especially as one approaches a spacelike singularity. Near the singularity, the geometry enters a regime governed by the BKL conjecture and characterized by a sequence of Kasner epochs and eras. To get a handle on the degrees of freedom involved in this evolution, I will introduce a monotonic function, known as the thermal a-function, which tracks the flow into the trans-IR region. With this function, I will show that the full sequence of Kasner epochs and eras can be effectively captured, and the degrees of freedom thin out and ultimately vanish at the trans-IR fixed point.
Posted by: Alan Rios Fukelman
Thu
25 Sep 2025
Bootstrapping Compton Amplitudes with Colour-Kinematics
📍 London
Andres Luna
(NBI Copenhagen)
Abstract:
In this talk, I will review the arbitrary-spin theory introduced in 2005.03071 to model spinning black holes in the post-Minkowskian approximation, and describe a procedure to systematically obtain Compton-like amplitudes in it, exploiting their factorization properties, and colour-kinematics duality. I will furthermore comment on the constraining of Wilson coefficients for arbitrary spinning bodies and its relation to colour-kinematic duality. This talk is based on 2503.22597.
In this talk, I will review the arbitrary-spin theory introduced in 2005.03071 to model spinning black holes in the post-Minkowskian approximation, and describe a procedure to systematically obtain Compton-like amplitudes in it, exploiting their factorization properties, and colour-kinematics duality. I will furthermore comment on the constraining of Wilson coefficients for arbitrary spinning bodies and its relation to colour-kinematic duality. This talk is based on 2503.22597.
Posted by: Nathan Moynihan
Wed
24 Sep 2025
Quantum dynamics meets quantum information
📍 London
Alexey Milekhin
(University of Kentucky)
Abstract:
Quantum computers have the potential to revolutionize both quantum simulations and classical computations. Rapid advancements in quantum hardware has not only introduced new opportunities but also posed significant theoretical challenges in understanding quantum dynamics. These developments highlight the need for benchmarking models—interacting many-body systems that can be solved exactly or numerically to assess the capabilities of quantum processors. In this talk, I will discuss powerful theoretical tools to address these challenges, focusing on the Sachdev–Ye–Kitaev (SYK) model and the emerging framework of entanglement in time, an information-theoretic approach designed to probe dynamical properties of quantum systems.
Quantum computers have the potential to revolutionize both quantum simulations and classical computations. Rapid advancements in quantum hardware has not only introduced new opportunities but also posed significant theoretical challenges in understanding quantum dynamics. These developments highlight the need for benchmarking models—interacting many-body systems that can be solved exactly or numerically to assess the capabilities of quantum processors. In this talk, I will discuss powerful theoretical tools to address these challenges, focusing on the Sachdev–Ye–Kitaev (SYK) model and the emerging framework of entanglement in time, an information-theoretic approach designed to probe dynamical properties of quantum systems.
Posted by: Evgeny Sobko
Mon
22 Sep 2025
Dimensional Transmutation and Confinement in Various Models
📍 London
Igor Klebanov
(Princeton University)
Abstract:
The talk will begin with a brief review of Quantum Chromodynamics (QCD) and the Confinement problem. Lattice Gauge Theory (LGT) provides a non-perturbative formulation of QCD, which has led to good numerical results for the low-lying hadron spectra. Yet, an analytical understanding of QCD is not available. I will then discuss several gauge theories which have some of the key features of QCD. One of them is based on the gauge/gravity duality and is described by the warped deformed conifold background of type IIB string theory. This theory exhibits confinement, and the quark-antiquark potential is similar to that found in LGT.
The 1+1 dimensional gauge theories have also served as useful models of quark confinement. I will revisit the classic Schwinger model and its lattice Hamiltonian formulation. A mass shift between the lattice and continuum definitions of mass, which is motivated by chiral symmetry, is shown to lead to improved results. I will also present the zero-temperature phase diagram of the two-flavor Schwinger model at theta=pi, which exhibits dimensional transmutation and spontaneous breaking of charge conjugation. Finally, I will discuss the 2D SU(N) gauge theory coupled to an adjoint multiplet of Majorana fermions. This model has a rich topological structure. I will introduce a Hamiltonian lattice approach to this gauge theory, in which one can compute the spectrum, the string tension, and other observables. The talk will end with some surprising exact results for this model.
The talk will begin with a brief review of Quantum Chromodynamics (QCD) and the Confinement problem. Lattice Gauge Theory (LGT) provides a non-perturbative formulation of QCD, which has led to good numerical results for the low-lying hadron spectra. Yet, an analytical understanding of QCD is not available. I will then discuss several gauge theories which have some of the key features of QCD. One of them is based on the gauge/gravity duality and is described by the warped deformed conifold background of type IIB string theory. This theory exhibits confinement, and the quark-antiquark potential is similar to that found in LGT.
The 1+1 dimensional gauge theories have also served as useful models of quark confinement. I will revisit the classic Schwinger model and its lattice Hamiltonian formulation. A mass shift between the lattice and continuum definitions of mass, which is motivated by chiral symmetry, is shown to lead to improved results. I will also present the zero-temperature phase diagram of the two-flavor Schwinger model at theta=pi, which exhibits dimensional transmutation and spontaneous breaking of charge conjugation. Finally, I will discuss the 2D SU(N) gauge theory coupled to an adjoint multiplet of Majorana fermions. This model has a rich topological structure. I will introduce a Hamiltonian lattice approach to this gauge theory, in which one can compute the spectrum, the string tension, and other observables. The talk will end with some surprising exact results for this model.
Posted by: Andreas Stergiou
Thu
18 Sep 2025
Extracting spinning two-body observables from S-matrix
📍 London
Canxin Shi
(Institute of Theoretical Physics, CAS (Beijing))
Abstract:
High-precision prediction of the two-body problem is at the center of gravitational-wave physics. I will present a novel method for extracting observables for two-body scattering systems from a set of generating functions, with full spin dependence. The approach uses the classical limit of the logarithm of the quantum S-matrix as generating functions. The 4-point matrix element of \(\log(S)\) gives the radial action, corresponding to conservative effects, whereas the higher-point contributions encode radiative information. The observables, such as momentum impulse, orbital angular momentum, and waveform, are obtained by applying differential operators, which are constructed from Dirac brackets and the generating functions, to the initial value of the observable. We demonstrate its power by calculating new high-precision results, including the impulse and spin kick for a probe in Kerr up to \(O(G^6 s^4)\), and the change in angular momentum for generic masses up to \(O(G^2 s^{11})\). Via analytic continuation, we can also provide information about bound orbits, such as their fundamental frequencies.
High-precision prediction of the two-body problem is at the center of gravitational-wave physics. I will present a novel method for extracting observables for two-body scattering systems from a set of generating functions, with full spin dependence. The approach uses the classical limit of the logarithm of the quantum S-matrix as generating functions. The 4-point matrix element of \(\log(S)\) gives the radial action, corresponding to conservative effects, whereas the higher-point contributions encode radiative information. The observables, such as momentum impulse, orbital angular momentum, and waveform, are obtained by applying differential operators, which are constructed from Dirac brackets and the generating functions, to the initial value of the observable. We demonstrate its power by calculating new high-precision results, including the impulse and spin kick for a probe in Kerr up to \(O(G^6 s^4)\), and the change in angular momentum for generic masses up to \(O(G^2 s^{11})\). Via analytic continuation, we can also provide information about bound orbits, such as their fundamental frequencies.
Posted by: Morteza S. Hosseini
Mon
15 Sep 2025
AI & the Future of Maths
📍 London
Yang-Hui He
(LIMS)
Abstract:
https://www.rigb.org/whats-on/mathematics-rise-machines
Royal Institution Public Lecture on AI & the future of Maths.
https://www.rigb.org/whats-on/mathematics-rise-machines
Royal Institution Public Lecture on AI & the future of Maths.
Posted by: Yang-Hui He
Mon
8 Sep 2025
South East Mathematical Seminar (SEMPS)
📍 South East
multiple speakers
Abstract:
LMS funded one-day seminar series: Speakers: Omer Gurdogan, Simon Ekhammar, Ida Zadeh, Mehran Jalali Farahani, Nika Sokolova
LMS funded one-day seminar series: Speakers: Omer Gurdogan, Simon Ekhammar, Ida Zadeh, Mehran Jalali Farahani, Nika Sokolova
Posted by: Alessandro Torrielli
Wed
3 Sep 2025
Spontaneous quantization of the Yang-Mills gradient flow
📍 London
Alexander Migdal
(IAS Princeton)
Abstract:
We formulate a nonsingular loop-space calculus for the Yang-Mills (YM) gradient flow, in which all variations act within the manifold of smooth loops via ``dot derivatives'' that are finite, parametrization-invariant, and free of cusp or backtracking singularities. This yields an exact momentum-loop representation and a universal trilinear loop-space diffusion equation, valid for any non-Abelian gauge group. We identify two distinct classes of exact solutions. The first is a self-dual (Hodge-dual) matrix-valued minimal surface whose area functional, when exponentiated, solves the fixed-point loop equation exactly, without contact terms or ambiguities; for planar loops the dual area equals \(2\sqrt{2}\) times the Euclidean minimal area, providing a geometrically grounded confinement mechanism. We also prove that the ordinary minimal surface in ℝ4 fails to satisfy the fixed-point loop equation, due to a singular nonvanishing contribution from the loop operator. The second is a decaying-flow solution in which the momentum loop performs a periodic random walk on regular star polygons – the ``Euler ensemble'' previously found in Navier-Stokes turbulence – realizing a form of spontaneous quantization in the YM gradient flow. We discuss the emergence of quantum-like Wilson-loop statistics from deterministic classical dynamics, potential implications for confinement in QCD, and the role of these fixed points as attractors in the space of YM gradient-flow trajectories.
We formulate a nonsingular loop-space calculus for the Yang-Mills (YM) gradient flow, in which all variations act within the manifold of smooth loops via ``dot derivatives'' that are finite, parametrization-invariant, and free of cusp or backtracking singularities. This yields an exact momentum-loop representation and a universal trilinear loop-space diffusion equation, valid for any non-Abelian gauge group. We identify two distinct classes of exact solutions. The first is a self-dual (Hodge-dual) matrix-valued minimal surface whose area functional, when exponentiated, solves the fixed-point loop equation exactly, without contact terms or ambiguities; for planar loops the dual area equals \(2\sqrt{2}\) times the Euclidean minimal area, providing a geometrically grounded confinement mechanism. We also prove that the ordinary minimal surface in ℝ4 fails to satisfy the fixed-point loop equation, due to a singular nonvanishing contribution from the loop operator. The second is a decaying-flow solution in which the momentum loop performs a periodic random walk on regular star polygons – the ``Euler ensemble'' previously found in Navier-Stokes turbulence – realizing a form of spontaneous quantization in the YM gradient flow. We discuss the emergence of quantum-like Wilson-loop statistics from deterministic classical dynamics, potential implications for confinement in QCD, and the role of these fixed points as attractors in the space of YM gradient-flow trajectories.
Posted by: Evgeny Sobko