Triangle Seminars
December 2026
Thu
17 Dec 2026
TBA
📍 London
Bipasha Chakraborty
(University of Southampton)
Abstract:
TBA
TBA
Posted by: Jack Araz
Thu
10 Dec 2026
Spatial projection of Kerr quasinormal modes from numerical data
📍 London
Lionel London
(KCL)
Abstract:
When two black holes merge, the newly formed black hole "rings down", like a struck bell, giving off gravitational waves that detectors such as LIGO can measure. The tones of this ringing, called quasinormal modes, are set entirely by the black hole's mass and spin. Measuring them is therefore one of the cleanest tests of Einstein's general relativity. The catch is that these modes are unusual. A guitar string's vibrations can be split into separate harmonics using the same idea as a Fourier series: each harmonic is orthogonal to the others, so you can "project" a vibration onto each one in turn. A ringing black hole loses energy as it rings, and its modes fade away. Ordinary orthogonality fails, so researchers usually resort to fitting curves to simulated signals. That can be unreliable when several modes overlap or the data are noisy. In this talk I will explain, with ideas familiar from linear algebra and Fourier analysis, how a clever change of basis makes black hole modes orthogonal again. This lets us project each mode straight out of computer-simulated data. I will show examples of the method recovering hidden and faint modes, and discuss what noise means for measuring them.
When two black holes merge, the newly formed black hole "rings down", like a struck bell, giving off gravitational waves that detectors such as LIGO can measure. The tones of this ringing, called quasinormal modes, are set entirely by the black hole's mass and spin. Measuring them is therefore one of the cleanest tests of Einstein's general relativity. The catch is that these modes are unusual. A guitar string's vibrations can be split into separate harmonics using the same idea as a Fourier series: each harmonic is orthogonal to the others, so you can "project" a vibration onto each one in turn. A ringing black hole loses energy as it rings, and its modes fade away. Ordinary orthogonality fails, so researchers usually resort to fitting curves to simulated signals. That can be unreliable when several modes overlap or the data are noisy. In this talk I will explain, with ideas familiar from linear algebra and Fourier analysis, how a clever change of basis makes black hole modes orthogonal again. This lets us project each mode straight out of computer-simulated data. I will show examples of the method recovering hidden and faint modes, and discuss what noise means for measuring them.
Posted by: Kymani Armstrong-Williams
Wed
9 Dec 2026
TBA
📍 London
Eric Perlmutter
(IPhT, Saclay)
Abstract:
TBA
TBA
Posted by: Kiarash Naderi
Wed
9 Dec 2026
TBA
📍 London
Deniz Bozkurt
(DESY)
Abstract:
TBA
TBA
Posted by: Elia de Sabbata
Thu
3 Dec 2026
TBD
📍 London
Matthew Roberts
(Iceland)
Abstract:
TBD
TBD
Posted by: Kymani Armstrong-Williams
Wed
2 Dec 2026
TBA
📍 London
Andrea Dei
(Southampton U.)
Abstract:
TBA
TBA
Posted by: Kiarash Naderi
Wed
2 Dec 2026
TBA
📍 London
Pavel Kovtun
Abstract:
TBA
TBA
Posted by: Elia de Sabbata
November 2026
Thu
26 Nov 2026
TBD
📍 London
Ella Cole
(Cambridge)
Abstract:
TBD
TBD
Posted by: Kymani Armstrong-Williams
Thu
19 Nov 2026
TBD
📍 London
Mattia Serrani
(Mons)
Abstract:
TBD.
TBD.
Posted by: Kymani Armstrong-Williams
Wed
18 Nov 2026
TBA
📍 London
Amit Sever
(Tel Aviv University)
Abstract:
TBA
TBA
Posted by: Kiarash Naderi
Wed
18 Nov 2026
TBA
📍 London
Kasia Budzik
(Harvard University)
Abstract:
TBA
TBA
Posted by: Elia de Sabbata
Thu
12 Nov 2026
TBD
📍 London
Lucile Cangemi
(Edinburgh)
Abstract:
TBD.
TBD.
Posted by: Kymani Armstrong-Williams
Wed
11 Nov 2026
Entanglement bootstrap for (edge) conformal field theories
📍 London
Xiang Li
(Oxford)
Abstract:
Entanglement bootstrap (EB) aims to uncover the universal data and structural properties of quantum many-body systems from local entanglement properties. In this talk, I will discuss our past progress on EB for 1+1D conformal field theories, including anomalous CFTs that can arise only as boundaries of 2+1D topological quantum field theories. Explicitly, I will discuss a locally checkable condition for 1+1D CFT ground states, as well as the reconstruction of Virasoro generators directly from the wavefunction. This allows us to diagnose if a given state is a CFT ground state or not, and if it is then how to extract CFT data from it.
Although these results are motivated by continuum field theory, they are also applicable to critical lattice systems. This opens the possibility of using entanglement bootstrap as a systematic framework for enumerating and potentially discovering new CFTs
Entanglement bootstrap (EB) aims to uncover the universal data and structural properties of quantum many-body systems from local entanglement properties. In this talk, I will discuss our past progress on EB for 1+1D conformal field theories, including anomalous CFTs that can arise only as boundaries of 2+1D topological quantum field theories. Explicitly, I will discuss a locally checkable condition for 1+1D CFT ground states, as well as the reconstruction of Virasoro generators directly from the wavefunction. This allows us to diagnose if a given state is a CFT ground state or not, and if it is then how to extract CFT data from it.
Although these results are motivated by continuum field theory, they are also applicable to critical lattice systems. This opens the possibility of using entanglement bootstrap as a systematic framework for enumerating and potentially discovering new CFTs
Posted by: Kiarash Naderi
Wed
11 Nov 2026
TBA
📍 London
Zimo Sun
(Institute for Advanced Study (IAS))
Abstract:
TBA
TBA
Posted by: Elia de Sabbata
Wed
11 Nov 2026
Chaos and thermalization in many-body Floquet systems
📍 London
Anton Kapustin
(Caltech)
Abstract:
Since the times of Ludwig Boltzmann, most physicists take it for granted that generic non-integrable closed dynamical systems, whether classical or quantum, thermalize at long times for generic initial conditions. Whether this belief is true or false depends on the type of systems one is willing to consider and the meaning of “generic” and “thermalizes”. In this talk I will discuss two types of many-body dynamical systems where thermalization (i.e. weak convergence to the state of maximal entropy) can be established for a large class of initial states. The first one is a system of an infinite number of spins with evolution generated by a repeated application of a Clifford Cellular Automaton. The second one is its classical counterpart and can be thought of as a mixing automorphism of an infinite-dimensional torus.
–-
Please register for the event!
https://lims.ac.uk/event/chaos-and-thermalisation-in-many-body-floquet-systems/
Colloquium at 5:00 PM, 11 Nov 2026 at LIMS, 2F of Royal Institution, 21 Albemarle St, W1S4BS, London
Everyone is warmly invited to stay for the reception afterwards, featuring drinks, cheese, refreshments, lively conversations, networking, and music in the evening!
Since the times of Ludwig Boltzmann, most physicists take it for granted that generic non-integrable closed dynamical systems, whether classical or quantum, thermalize at long times for generic initial conditions. Whether this belief is true or false depends on the type of systems one is willing to consider and the meaning of “generic” and “thermalizes”. In this talk I will discuss two types of many-body dynamical systems where thermalization (i.e. weak convergence to the state of maximal entropy) can be established for a large class of initial states. The first one is a system of an infinite number of spins with evolution generated by a repeated application of a Clifford Cellular Automaton. The second one is its classical counterpart and can be thought of as a mixing automorphism of an infinite-dimensional torus.
–-
Please register for the event!
https://lims.ac.uk/event/chaos-and-thermalisation-in-many-body-floquet-systems/
Colloquium at 5:00 PM, 11 Nov 2026 at LIMS, 2F of Royal Institution, 21 Albemarle St, W1S4BS, London
Everyone is warmly invited to stay for the reception afterwards, featuring drinks, cheese, refreshments, lively conversations, networking, and music in the evening!
Posted by: JUVEN WANG
Thu
5 Nov 2026
Simulating a 3D U(1) gauge theory on a digital quantum computer
📍 London
Gurtej Kanwar
(University of Edinburgh)
Abstract:
I will discuss a recent simulation carried out on IBM Quantum hardware of the real-time dynamics in the 3D U(1) gauge theory. This theory serves as an interesting testbed for quantum simulations of field theories, as it features confinement and non-trivial string dynamics. A tailor-made quantum-link representation of the field theory is used to map naturally onto the heavy-hex quantum architecture used for the calculation. I discuss the results obtained and their interpretation in the context of the field theory dynamics.
I will discuss a recent simulation carried out on IBM Quantum hardware of the real-time dynamics in the 3D U(1) gauge theory. This theory serves as an interesting testbed for quantum simulations of field theories, as it features confinement and non-trivial string dynamics. A tailor-made quantum-link representation of the field theory is used to map naturally onto the heavy-hex quantum architecture used for the calculation. I discuss the results obtained and their interpretation in the context of the field theory dynamics.
Posted by: Jack Araz
Thu
5 Nov 2026
TBD
📍 London
Andreas Stergiou
(KCL)
Abstract:
TBD.
TBD.
Posted by: Kymani Armstrong-Williams
Wed
4 Nov 2026
Gravity in a conformal box
📍 London
Silvia Georgescu
(King's Coll. London)
Abstract:
We investigate gravitational dynamics in the presence of finite timelike boundaries with conformal boundary conditions. We focus on the limit in which the conformal boundary approaches a black hole or cosmological horizon. In this regime, potentially exponentially growing perturbations are attenuated, and we find a hierarchy of modes localized near the conformal boundary. In particular, we uncover sound and shear modes that admit an interpretation in terms of a conformal fluid with shear-viscosity-to-entropy-density ratio \eta/s=1/(4\pi). For the AdS4 black brane, we track these modes numerically as the boundary is moved from the near-horizon region towards the asymptotic AdS boundary, and find that they continuously connect to the hydrodynamic sound and shear modes of the fluid/gravity correspondence.
We investigate gravitational dynamics in the presence of finite timelike boundaries with conformal boundary conditions. We focus on the limit in which the conformal boundary approaches a black hole or cosmological horizon. In this regime, potentially exponentially growing perturbations are attenuated, and we find a hierarchy of modes localized near the conformal boundary. In particular, we uncover sound and shear modes that admit an interpretation in terms of a conformal fluid with shear-viscosity-to-entropy-density ratio \eta/s=1/(4\pi). For the AdS4 black brane, we track these modes numerically as the boundary is moved from the near-horizon region towards the asymptotic AdS boundary, and find that they continuously connect to the hydrodynamic sound and shear modes of the fluid/gravity correspondence.
Posted by: Kiarash Naderi
Mon
2 Nov 2026
Lonti: Bootstrapping String Theory (4/4)
📍 London
Shai Chester
(Imperial College)
Abstract:
We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.
We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.
Posted by: Damian Galante
October 2026
Fri
30 Oct 2026
Hadron scattering at Large N
📍 London
Sebastiano Bocchia
(City St George's, U. of London)
Abstract:
In this talk I will review my recent paper arXiv:2610.31578 on bootstrapping large N hadron scattering amplitudes. This generalizes the large N Bootstrap of Albert and Rastelli to massive pions and glueballs. At large N, unitarity becomes positivity, and crossing symmetry enforces null constraints on the amplitudes. I will discuss our bounds, and how the extremal spectra compare with our expectations based on lattice and experimental data.
In this talk I will review my recent paper arXiv:2610.31578 on bootstrapping large N hadron scattering amplitudes. This generalizes the large N Bootstrap of Albert and Rastelli to massive pions and glueballs. At large N, unitarity becomes positivity, and crossing symmetry enforces null constraints on the amplitudes. I will discuss our bounds, and how the extremal spectra compare with our expectations based on lattice and experimental data.
Posted by: Andrea Guerrieri
Wed
28 Oct 2026
Decoupling saddles of the gravitational index and the Farey tail
📍 London
Davide Cassani
(INFN, Padua)
Abstract:
The talk explores the relation between gravitational saddles computing supersymmetric indices in asymptotically flat and AdS spacetimes, focusing on the D1-D5 system. Starting from five-dimensional saddles of the gravitational supersymmetric index, I will describe how a type IIB uplift and a decoupling limit yield asymptotically AdS_3 × S^3 configurations. These include horizonless geometries associated with fractional spectral flow in the dual CFT_2, and families of black hole saddles related by modular transformations. The construction extends the familiar modular family of BTZ black holes to backgrounds with nontrivial orbifold identifications and establishes their asymptotically flat origin. Their on-shell actions, including nontrivial modular phases, precisely match the corresponding contributions to the Farey-tail expansion of the D1-D5 elliptic genus, providing a sharp connection between gravitational saddles and microscopic counting.
The talk explores the relation between gravitational saddles computing supersymmetric indices in asymptotically flat and AdS spacetimes, focusing on the D1-D5 system. Starting from five-dimensional saddles of the gravitational supersymmetric index, I will describe how a type IIB uplift and a decoupling limit yield asymptotically AdS_3 × S^3 configurations. These include horizonless geometries associated with fractional spectral flow in the dual CFT_2, and families of black hole saddles related by modular transformations. The construction extends the familiar modular family of BTZ black holes to backgrounds with nontrivial orbifold identifications and establishes their asymptotically flat origin. Their on-shell actions, including nontrivial modular phases, precisely match the corresponding contributions to the Farey-tail expansion of the D1-D5 elliptic genus, providing a sharp connection between gravitational saddles and microscopic counting.
Posted by: Kiarash Naderi
Wed
28 Oct 2026
The flat limit of double holography
📍 London
Dominik Neuenfeld
(University of Würzburg)
Abstract:
I explain how to take a well-defined flat-space limit of brane models of AdS coupled to a non-gravitating bath. In the dual BCFT this amounts to a triple-scaling limit where both the number of boundary degrees of freedom and the boundary coupling are taken to infinity while the BCFT boundary piecewise approaches a lightcone. This procedure acts on the conformal generators as a Wigner-İnönü contraction, reducing the global BCFT symmetry algebra to the global symmetry algebra of flat space.
I will discuss two natural notions of entanglement entropy of the flat-space dual. These are distinguished by whether modes that have left through future null infinity are included or not and give rise to a vanishing and non-trivial Page curve, respectively. Taking the flat-space limit of topological black holes, the Page time remains finite in two-dimensions. In d > 2 the Page time diverges in the flat limit, since AdS topological black holes become flat-space Rindler horizons.
I explain how to take a well-defined flat-space limit of brane models of AdS coupled to a non-gravitating bath. In the dual BCFT this amounts to a triple-scaling limit where both the number of boundary degrees of freedom and the boundary coupling are taken to infinity while the BCFT boundary piecewise approaches a lightcone. This procedure acts on the conformal generators as a Wigner-İnönü contraction, reducing the global BCFT symmetry algebra to the global symmetry algebra of flat space.
I will discuss two natural notions of entanglement entropy of the flat-space dual. These are distinguished by whether modes that have left through future null infinity are included or not and give rise to a vanishing and non-trivial Page curve, respectively. Taking the flat-space limit of topological black holes, the Page time remains finite in two-dimensions. In d > 2 the Page time diverges in the flat limit, since AdS topological black holes become flat-space Rindler horizons.
Posted by: Elia de Sabbata
Tue
27 Oct 2026
Shock formation in decelerated spacetimes
📍 London
Maximilian Ofner
(Cambridge)
Abstract:
In cosmological models the matter content of the universe is assumed to be a compressible fluid. Such fluids are prone to the formation of so-called shock singularities, meaning that, at a finite time, the fluid gradient blows up, while the fluid quantities themselves stay bounded. By contrast, rapidly expanding spacetimes facilitate stabilization of any fluid contained inside. This dichotomy raises the question: What amount of expansion is sufficient to prevent shocks forming for sufficiently small data? At the beginning of this talk, we will discuss the preliminaries of relativistic fluids as an initial value problem. Afterwards, I will present new results in the regime of decelerated expansion, which seek to answer this central question. This is joint work with Todd Oliynyk.
In cosmological models the matter content of the universe is assumed to be a compressible fluid. Such fluids are prone to the formation of so-called shock singularities, meaning that, at a finite time, the fluid gradient blows up, while the fluid quantities themselves stay bounded. By contrast, rapidly expanding spacetimes facilitate stabilization of any fluid contained inside. This dichotomy raises the question: What amount of expansion is sufficient to prevent shocks forming for sufficiently small data? At the beginning of this talk, we will discuss the preliminaries of relativistic fluids as an initial value problem. Afterwards, I will present new results in the regime of decelerated expansion, which seek to answer this central question. This is joint work with Todd Oliynyk.
Posted by: Alan Rios Fukelman
Mon
26 Oct 2026
Lonti: Bootstrapping String Theory (3/4)
📍 London
Shai Chester
(Imperial College)
Abstract:
We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.
We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.
Posted by: Damian Galante
Thu
22 Oct 2026
Scattering in Phase Space: Eikonals, Radiation and Quantum Geometry
📍 London
Nathan Moynihan
(Edinburgh)
Abstract:
How do classical trajectories and radiation emerge from quantum
scattering? I will discuss a phase-space approach to this question,
which treats the trajectories of scattering bodies and their emitted
radiation via a common eikonal-like footing. This provides a natural
bridge between amplitudes, eikonal scattering and classical waveforms,
and suggests a broader quantum-classical geometric picture of
scattering in which matter and radiation intertwine in an interesting
way that we will explore.
How do classical trajectories and radiation emerge from quantum
scattering? I will discuss a phase-space approach to this question,
which treats the trajectories of scattering bodies and their emitted
radiation via a common eikonal-like footing. This provides a natural
bridge between amplitudes, eikonal scattering and classical waveforms,
and suggests a broader quantum-classical geometric picture of
scattering in which matter and radiation intertwine in an interesting
way that we will explore.
Posted by: Kymani Armstrong-Williams
Wed
21 Oct 2026
The Critical Collapse of a Perfect Fluid in Infinite Dimensions
📍 London
Craig Clark
(Pisa, Scuola Normale Superiore)
Abstract:
I will review a series of impressive numerical calculations from the 90s that revealed universal scaling behaviour in gravitational collapse. I will then focus on spherically symmetric perfect fluid collapse and explain how treating the number of spacetime dimensions, D, as an expansion parameter gives us analytic control of its continuously self-similar critical solution. In a 1/D expansion, we construct this solution and compute its critical exponent. At leading order, the length-scaling exponent is 1/2 and does not depend on the fluid’s equation of state parameter, a simplification reminiscent of mean-field behaviour. This rich system provides many potential routes for exploring universality in classical gravity. Based on a series of forthcoming papers with Guilherme L. Pimentel.
I will review a series of impressive numerical calculations from the 90s that revealed universal scaling behaviour in gravitational collapse. I will then focus on spherically symmetric perfect fluid collapse and explain how treating the number of spacetime dimensions, D, as an expansion parameter gives us analytic control of its continuously self-similar critical solution. In a 1/D expansion, we construct this solution and compute its critical exponent. At leading order, the length-scaling exponent is 1/2 and does not depend on the fluid’s equation of state parameter, a simplification reminiscent of mean-field behaviour. This rich system provides many potential routes for exploring universality in classical gravity. Based on a series of forthcoming papers with Guilherme L. Pimentel.
Posted by: Kiarash Naderi
Wed
21 Oct 2026
Twisted BPS decoupling limits and AdS/CFT
📍 London
Troels Harmark
(Niels Bohr Institute)
Abstract:
BPS decoupling limits of string and M-theory have led to profound insights into gravity and non-perturbative quantum theory, most notably with the AdS/CFT correspondence. A large class of such limits are related by U-duality to discrete lightcone quantization limits (DLCQs). However, there are natural BPS decoupling limits within the AdS/CFT correspondence that cannot be seen as DLCQ limits. Therefore, we introduce a new kind of BPS decoupling limit in which the relevant BPS states carry momentum along circle fibers geometrically twisted over a base space, unlike for a DLCQ limit. In the AdS/CFT correspondence these limits are associated with BPS states of the global symmetry algebra PSU(2,2|4). In general, string fluctuations in a twisted BPS decoupling limit are described by non-relativistic sigma-models on emergent non-Lorentzian target spaces with a natural symplectic structure. This further supports the broader connection between BPS limits and non-Lorentzian geometry. We introduce analogous limits of D-branes as well, probing the same symplectic structure as the string. For AdS/CFT, these results point to corners with tractable and explicit quantum-mechanical descriptions of non-perturbative regimes.
BPS decoupling limits of string and M-theory have led to profound insights into gravity and non-perturbative quantum theory, most notably with the AdS/CFT correspondence. A large class of such limits are related by U-duality to discrete lightcone quantization limits (DLCQs). However, there are natural BPS decoupling limits within the AdS/CFT correspondence that cannot be seen as DLCQ limits. Therefore, we introduce a new kind of BPS decoupling limit in which the relevant BPS states carry momentum along circle fibers geometrically twisted over a base space, unlike for a DLCQ limit. In the AdS/CFT correspondence these limits are associated with BPS states of the global symmetry algebra PSU(2,2|4). In general, string fluctuations in a twisted BPS decoupling limit are described by non-relativistic sigma-models on emergent non-Lorentzian target spaces with a natural symplectic structure. This further supports the broader connection between BPS limits and non-Lorentzian geometry. We introduce analogous limits of D-branes as well, probing the same symplectic structure as the string. For AdS/CFT, these results point to corners with tractable and explicit quantum-mechanical descriptions of non-perturbative regimes.
Posted by: Elia de Sabbata
Wed
21 Oct 2026
Can one hear the shape of a black hole singularity?
📍 London
Sean Hartnoll
(Cambridge U)
Abstract:
Black holes contain spacetime singularities, at which tidal forces become infinite and time ends. The approach to these singularities is believed to be chaotic and yet governed, on average, by a deep number-theoretic symmetry known as modularity. The outside of a black hole, in contrast, is highly regular. Any feature is rapidly hoovered up by the black hole itself and an external observer will witness only a "ringdown", the wobbles of the event horizon as it returns to equilibrium. A low-frequency so-called "quasinormal mode" of this ringdown was detected in 2015 by gravitational wave experiments. It has been known for two decades that very high frequency quasinormal modes are sensitive to the behaviour of spacetime close to the singularity, via a mathematical process known as analytic continuation. I will explain recent work that has shown how the chaotic near-singularity dynamics can be heard by listening carefully to the quasinormal modes.
–-
Please register for the event:
https://lims.ac.uk/event/can-one-hear-the-shape-of-a-black-hole-singularity/
Colloquium at 4:30 PM, 21 Oct 2026 at LIMS, 2F of Royal Institution, 21 Albemarle St, W1S4BS, London.
Attendees are welcome to stay for the reception after with drinks, cheese, and eateries.
Black holes contain spacetime singularities, at which tidal forces become infinite and time ends. The approach to these singularities is believed to be chaotic and yet governed, on average, by a deep number-theoretic symmetry known as modularity. The outside of a black hole, in contrast, is highly regular. Any feature is rapidly hoovered up by the black hole itself and an external observer will witness only a "ringdown", the wobbles of the event horizon as it returns to equilibrium. A low-frequency so-called "quasinormal mode" of this ringdown was detected in 2015 by gravitational wave experiments. It has been known for two decades that very high frequency quasinormal modes are sensitive to the behaviour of spacetime close to the singularity, via a mathematical process known as analytic continuation. I will explain recent work that has shown how the chaotic near-singularity dynamics can be heard by listening carefully to the quasinormal modes.
–-
Please register for the event:
https://lims.ac.uk/event/can-one-hear-the-shape-of-a-black-hole-singularity/
Colloquium at 4:30 PM, 21 Oct 2026 at LIMS, 2F of Royal Institution, 21 Albemarle St, W1S4BS, London.
Attendees are welcome to stay for the reception after with drinks, cheese, and eateries.
Posted by: JUVEN WANG
Tue
20 Oct 2026
TBA
📍 London
Klaas Parmentier
(Cambridge)
Abstract:
TBA
TBA
Posted by: Alan Rios Fukelman
Mon
19 Oct 2026
Lonti: Bootstrapping String Theory (2/4)
📍 London
Shai Chester
(Imperial College)
Abstract:
We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.
We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.
Posted by: Damian Galante
Mon
19 Oct 2026
AI and the process of human mathematics
📍 London
Geordie Williamson
(LIMS)
Abstract:
Registration Please fill in this form https://tally.so/r/rj7axl to confirm your attendance at Geordie’s talk, so we have a clearer idea of numbers. It's free but due to popularity please sign up.
Almost every week brings another AI breakthrough in mathematics—and fresh questions about the future of the field, its practitioners and humanity itself. In this AI for Mathematical Sciences seminar, Prof. Geordie Williamson sets aside predictions about what AI might achieve and turns instead to how humans do mathematics.
Williamson examines the choices and intuitions that shape mathematical thought. He considers where definitions come from, what purpose they serve and how they help mathematicians explore unfamiliar ideas. He also explores the role of prediction in research, from recognising patterns to anticipating what might be true.
Finally, he considers whether geometry plays a fundamental part in mathematics, even in areas far removed from shapes and space. Rather than forecasting what machines may soon prove, the talk takes AI’s rise as an occasion to reflect on the human mathematical process: how mathematicians think, what guides their work and what they value in it.
Registration Please fill in this form https://tally.so/r/rj7axl to confirm your attendance at Geordie’s talk, so we have a clearer idea of numbers. It's free but due to popularity please sign up.
Almost every week brings another AI breakthrough in mathematics—and fresh questions about the future of the field, its practitioners and humanity itself. In this AI for Mathematical Sciences seminar, Prof. Geordie Williamson sets aside predictions about what AI might achieve and turns instead to how humans do mathematics.
Williamson examines the choices and intuitions that shape mathematical thought. He considers where definitions come from, what purpose they serve and how they help mathematicians explore unfamiliar ideas. He also explores the role of prediction in research, from recognising patterns to anticipating what might be true.
Finally, he considers whether geometry plays a fundamental part in mathematics, even in areas far removed from shapes and space. Rather than forecasting what machines may soon prove, the talk takes AI’s rise as an occasion to reflect on the human mathematical process: how mathematicians think, what guides their work and what they value in it.
Posted by: Yang-Hui He
Thu
15 Oct 2026
Mixed Schur–Weyl Duality and Topological Expansions for 2D Gauge Theory revisited
📍 London
Antoine Dalqvist
(Sussex)
Abstract:
This talk explores the role of Schur–Weyl duality between unitary and symmetric groups in random matrix theory and the large-N limits of lattice gauge theories, from a combinatorial perspective.
I shall present a combinatorial approach based on a variant of Schur–Weyl duality for mixed tensors, recently used to establish asymptotic expansions of the partition function and convergence of Wilson loops in two-dimensional Yang–Mills theory. I will revisit the work of Gross and Taylor, “2D QCD Is a String Theory,” sketch an alternative proof of a formula due to Kimura and Ramgoolam, and discuss applications to surface expansions of Wilson loops and the determination of the master field on closed orientable surfaces.
This talk is based on the arXiv preprint arXiv:2603.1137.
This talk explores the role of Schur–Weyl duality between unitary and symmetric groups in random matrix theory and the large-N limits of lattice gauge theories, from a combinatorial perspective.
I shall present a combinatorial approach based on a variant of Schur–Weyl duality for mixed tensors, recently used to establish asymptotic expansions of the partition function and convergence of Wilson loops in two-dimensional Yang–Mills theory. I will revisit the work of Gross and Taylor, “2D QCD Is a String Theory,” sketch an alternative proof of a formula due to Kimura and Ramgoolam, and discuss applications to surface expansions of Wilson loops and the determination of the master field on closed orientable surfaces.
This talk is based on the arXiv preprint arXiv:2603.1137.
Posted by: Kymani Armstrong-Williams
Wed
14 Oct 2026
Triangle: From Asymptotic Symmetries to Infinite Symmetry Algebras in Conformal Field Theory
📍 London
Monica Pate
(NYU)
Abstract:
Please register here: https://forms.gle/7zfqxHjCDSdDesmy7
The recent discovery of a known infinite-dimensional algebra, w(1+infinity), among the asymptotic symmetries of four-dimensional asymptotically flat spacetimes has been interpreted as key evidence in support of a bottom-up approach to flat-space (a.k.a. celestial) holography. In particular, since a holographic theory must realize the symmetries of its associated gravitational dual, large universal symmetries in principle impose fairly stringent constraints on a holographic correspondence. Of course, concrete progress relies crucially on the precise strength of the constraints from symmetry. Thus in pursuit of this larger goal, in this seminar, I will present a precise avatar of the universal w(1+infinity) symmetry algebra that persists in the absence of gravity and in particular is realized in generic interacting four-dimensional conformal field theories. The generators of the algebra are light-ray operators formed from null integrals of the stress tensor that generalize the average null energy operator. I will discuss potential implications for conformal field theories in spacetime dimensions greater than two and celestial holography.
Please register here: https://forms.gle/7zfqxHjCDSdDesmy7
The recent discovery of a known infinite-dimensional algebra, w(1+infinity), among the asymptotic symmetries of four-dimensional asymptotically flat spacetimes has been interpreted as key evidence in support of a bottom-up approach to flat-space (a.k.a. celestial) holography. In particular, since a holographic theory must realize the symmetries of its associated gravitational dual, large universal symmetries in principle impose fairly stringent constraints on a holographic correspondence. Of course, concrete progress relies crucially on the precise strength of the constraints from symmetry. Thus in pursuit of this larger goal, in this seminar, I will present a precise avatar of the universal w(1+infinity) symmetry algebra that persists in the absence of gravity and in particular is realized in generic interacting four-dimensional conformal field theories. The generators of the algebra are light-ray operators formed from null integrals of the stress tensor that generalize the average null energy operator. I will discuss potential implications for conformal field theories in spacetime dimensions greater than two and celestial holography.
Posted by: Damian Galante
Wed
14 Oct 2026
Triangle: Quantum gravity fluctuations at long distances
📍 London
Ben Freivogel
(University of Amsterdam)
Abstract:
Please register here: https://forms.gle/7zfqxHjCDSdDesmy7
I will address the question: In what situations are perturbative quantum gravity effects important at distances much longer than the Planck scale? Among other examples, I will calculate the `quantum width' of the black hole horizon.
Please register here: https://forms.gle/7zfqxHjCDSdDesmy7
I will address the question: In what situations are perturbative quantum gravity effects important at distances much longer than the Planck scale? Among other examples, I will calculate the `quantum width' of the black hole horizon.
Posted by: Damian Galante
Tue
13 Oct 2026
Causality and instability in holographic Gauss-Bonnet gravity
📍 London
Pavel Kovtun
(Southampton)
Abstract:
TBA
TBA
Posted by: Alan Rios Fukelman
Mon
12 Oct 2026
Lonti: Bootstrapping String Theory (1/4)
📍 London
Shai Chester
(Imperial College)
Abstract:
We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.
We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.
Posted by: Damian Galante
Fri
9 Oct 2026
QFT in AdS
📍 London
Jiaxin Qiao
(Kavli IPMU)
Abstract:
QFT in anti-de Sitter space (AdS) provides a useful setting in which problems in strongly coupled QFT can be reformulated in terms of discrete spectral data and boundary correlation functions. In this informal discussion, I will give an elementary introduction to this point of view, aimed at people who are interested in learning what QFT in AdS is useful for and what kinds of problems are currently being studied.
I will begin with the basic motivation for placing an ordinary QFT on a fixed AdS background, and explain how the AdS curvature introduces a useful infrared scale while preserving a large symmetry group. I will then discuss some of the main quantities one would like to determine, such as the energy spectrum, boundary OPE data, bulk observables, and their relation to the flat-space S-matrix.
I will try to cover several approaches to these questions, focusing in particular on conformal bootstrap ideas, Hamiltonian truncation, and a recent ODE-based approach in which QFT data are evolved under deformations of the theory. If time permits, I will also comment on bulk locality and on the flat-space limit. The goal is not to give a comprehensive review, but rather to explain the basic ideas and some open questions to people who would like to get a first introduction to this topic.
QFT in anti-de Sitter space (AdS) provides a useful setting in which problems in strongly coupled QFT can be reformulated in terms of discrete spectral data and boundary correlation functions. In this informal discussion, I will give an elementary introduction to this point of view, aimed at people who are interested in learning what QFT in AdS is useful for and what kinds of problems are currently being studied.
I will begin with the basic motivation for placing an ordinary QFT on a fixed AdS background, and explain how the AdS curvature introduces a useful infrared scale while preserving a large symmetry group. I will then discuss some of the main quantities one would like to determine, such as the energy spectrum, boundary OPE data, bulk observables, and their relation to the flat-space S-matrix.
I will try to cover several approaches to these questions, focusing in particular on conformal bootstrap ideas, Hamiltonian truncation, and a recent ODE-based approach in which QFT data are evolved under deformations of the theory. If time permits, I will also comment on bulk locality and on the flat-space limit. The goal is not to give a comprehensive review, but rather to explain the basic ideas and some open questions to people who would like to get a first introduction to this topic.
Posted by: Andrea Guerrieri
Fri
9 Oct 2026
Are All Phase Transitions of Landau Type in Disguise?
📍 London
Sakura Schafer-Nameki
(Oxford)
Abstract:
The answer is no. Landau's paradigm characterizes phases of matter by their pattern of spontaneous symmetry breaking, traditionally for groups, and has more recently been extended to so-called non-invertible or categorical symmetries. In this colloquium we will see how recent insights into these new symmetries teach us even new things about ordinary group symmetries.
Central to this endeavour is the symmetry topological field theory (SymTFT), which conveniently separates symmetry from dynamics. Gapped phases correspond to topological boundary conditions of the SymTFT, their order parameters, local operators as well as string-operators, to the topological lines in the SymTFT, and phase transitions to condensable algebras.
Many transitions that appear to be beyond Landau, such as transitions between symmetry-protected topological (SPT) phases and certain deconfined quantum critical points in 1+1d, become symmetry-breaking transitions, i.e. of Landau type, after gauging. This may hint at the possibility that all transitions are, after suitable gauging and other manipulations, of Landau symmetry-breaking type. I will explain how, with the help of the SymTFT, we can uncover phase transitions which do not admit any dual frame that would make them of Landau type. Such so-called twin phase transitions occur already for finite groups. This brings us full circle: even for group symmetries, we can learn something new from the recent developments in generalized and categorical symmetries.
–-
Colloquium at 3 PM, 9 Oct 2026
https://lims.ac.uk/event/are-all-phase-transitions-of-landau-type-in-disguise/
The answer is no. Landau's paradigm characterizes phases of matter by their pattern of spontaneous symmetry breaking, traditionally for groups, and has more recently been extended to so-called non-invertible or categorical symmetries. In this colloquium we will see how recent insights into these new symmetries teach us even new things about ordinary group symmetries.
Central to this endeavour is the symmetry topological field theory (SymTFT), which conveniently separates symmetry from dynamics. Gapped phases correspond to topological boundary conditions of the SymTFT, their order parameters, local operators as well as string-operators, to the topological lines in the SymTFT, and phase transitions to condensable algebras.
Many transitions that appear to be beyond Landau, such as transitions between symmetry-protected topological (SPT) phases and certain deconfined quantum critical points in 1+1d, become symmetry-breaking transitions, i.e. of Landau type, after gauging. This may hint at the possibility that all transitions are, after suitable gauging and other manipulations, of Landau symmetry-breaking type. I will explain how, with the help of the SymTFT, we can uncover phase transitions which do not admit any dual frame that would make them of Landau type. Such so-called twin phase transitions occur already for finite groups. This brings us full circle: even for group symmetries, we can learn something new from the recent developments in generalized and categorical symmetries.
–-
Colloquium at 3 PM, 9 Oct 2026
https://lims.ac.uk/event/are-all-phase-transitions-of-landau-type-in-disguise/
Posted by: JUVEN WANG
Thu
8 Oct 2026
All-Plus QED Wavefunctions in de Sitter Space
📍 London
Jiajie Mei
(Amsterdam)
Abstract:
I will discuss tree-level wavefunction coefficients in scalar QED in four-dimensional de Sitter space, focusing on a charged scalar pair coupled to an arbitrary number of positive-helicity photons. We find a remarkably simple all-multiplicity structure for these coefficients. I will present the resulting compact formula and explain how its analytic structure, Abelian Ward identities, and conformal symmetry lead to an exact recursion.
I will discuss tree-level wavefunction coefficients in scalar QED in four-dimensional de Sitter space, focusing on a charged scalar pair coupled to an arbitrary number of positive-helicity photons. We find a remarkably simple all-multiplicity structure for these coefficients. I will present the resulting compact formula and explain how its analytic structure, Abelian Ward identities, and conformal symmetry lead to an exact recursion.
Posted by: Kymani Armstrong-Williams
Wed
7 Oct 2026
Proliferation Transitions for Non-Abelian Anyons
📍 London
Andrea Antinucci
(Oxford U., Inst. Math.)
Abstract:
Phases of matter and the transitions between them are famously characterized within the Landau paradigm and Landau–Ginzburg theory: phases are labeled by broken or unbroken symmetries, while phase transitions are described in terms of scalar order parameters. There are, however, phases beyond the standard Landau paradigm that are distinguished not by the realization of ordinary symmetries, but by that of generalized global symmetries. Among these, topologically ordered phases in (2+1)d possess non-invertible 1-form symmetries described by anyon lines. In this talk, I will present a framework for describing transitions between topologically ordered phases related by anyon proliferation, which can be viewed as a non-invertible generalization of the choice of the unbroken symmetry. The resulting theories involve scalar fields coupled to gauge fields. A crucial ingredient in this construction is the (3+1)d Symmetry Topological Field Theory (SymTFT), which allows to separate symmetry from dynamics and will be employed in a rather unconventional way.
Phases of matter and the transitions between them are famously characterized within the Landau paradigm and Landau–Ginzburg theory: phases are labeled by broken or unbroken symmetries, while phase transitions are described in terms of scalar order parameters. There are, however, phases beyond the standard Landau paradigm that are distinguished not by the realization of ordinary symmetries, but by that of generalized global symmetries. Among these, topologically ordered phases in (2+1)d possess non-invertible 1-form symmetries described by anyon lines. In this talk, I will present a framework for describing transitions between topologically ordered phases related by anyon proliferation, which can be viewed as a non-invertible generalization of the choice of the unbroken symmetry. The resulting theories involve scalar fields coupled to gauge fields. A crucial ingredient in this construction is the (3+1)d Symmetry Topological Field Theory (SymTFT), which allows to separate symmetry from dynamics and will be employed in a rather unconventional way.
Posted by: Kiarash Naderi
September 2026
Wed
30 Sep 2026
Two-point functions in 4 − 2 epsilon dimensions from localization
📍 London
Alessandro Georgoudis
(Queen Mary, U. of London)
Abstract:
In this talk I will present some recent developments where supersymmetric localization is used to study two-point functions of half-BPS operators in maximally supersymmetric Yang-Mills theory continued to (d=4-2epsilon) dimensions. I will describe how the epsilon-expansion of these correlators can be extracted from matrix-model computations on (S^d), leading to all-loop results in the planar limit and to extensions at finite N and higher charge. I will then compare these localization predictions with direct perturbative calculations in flat space. While the two approaches agree at order epsilon, after accounting for the Fourier transform between position and momentum space, a non-trivial mismatch appears at higher orders. Finally, I will explain how, for the dimension-two operator, this mismatch can be used to conjecture an all-loop formula at order epsilon^2 in flat space.
In this talk I will present some recent developments where supersymmetric localization is used to study two-point functions of half-BPS operators in maximally supersymmetric Yang-Mills theory continued to (d=4-2epsilon) dimensions. I will describe how the epsilon-expansion of these correlators can be extracted from matrix-model computations on (S^d), leading to all-loop results in the planar limit and to extensions at finite N and higher charge. I will then compare these localization predictions with direct perturbative calculations in flat space. While the two approaches agree at order epsilon, after accounting for the Fourier transform between position and momentum space, a non-trivial mismatch appears at higher orders. Finally, I will explain how, for the dimension-two operator, this mismatch can be used to conjecture an all-loop formula at order epsilon^2 in flat space.
Posted by: Kiarash Naderi
Wed
30 Sep 2026
Distinguishing Topological Phases with Partition Functions
📍 London
Alex Turzillo
(DAMTP)
Abstract:
I'll discuss a connection between topological field theories and topological phases of lattice models, which shows how partition functions of field theories can inspire order parameters for lattice models. After some generalities, I'll use this connection to develop, out of lens space partition functions, a novel order parameter for distinguishing two-dimensional symmetry protected topological (SPT) phases. The resulting procedure takes a wavefunction, such as a ground state of a lattice model, and detects its SPT invariants as expectation values of finitely supported operators, similar to how string order parameters work for 1D SPT phases.
I'll discuss a connection between topological field theories and topological phases of lattice models, which shows how partition functions of field theories can inspire order parameters for lattice models. After some generalities, I'll use this connection to develop, out of lens space partition functions, a novel order parameter for distinguishing two-dimensional symmetry protected topological (SPT) phases. The resulting procedure takes a wavefunction, such as a ground state of a lattice model, and detects its SPT invariants as expectation values of finitely supported operators, similar to how string order parameters work for 1D SPT phases.
Posted by: Elia de Sabbata
Wed
30 Sep 2026
Model Theory and the Hypothesis of a Finite Universe
📍 London
Boris Zilber
(Oxford)
Abstract:
Could the apparently continuous world of mathematics and physics be an approximation to a fundamentally finite universe? Boris Zilber explores this question through model theory, a branch of mathematics that studies theories and their models.
The lectures introduce the notion of global approximation: rather than viewing a finite model simply as a local discretisation of a continuous theory, one asks whether a single large finite structure can approximate an entire continuous structure globally. Zilber will describe how this perspective leads to compact complex structures and discuss its possible implications for spacetime and fundamental physics. Examples will include finite cyclic models of spacetime, Lorentz symmetry, quantum mechanics and string-theoretic structures. The lectures will also consider the distinction between the global mathematical structure and the local coordinates and measurements reconstructed by an observer.
Boris Zilber is Professor Emeritus of Mathematical Logic at the University of Oxford. His research is in model theory, geometry and their connections with other areas of mathematics and physics. He is one of the founders of geometric stability theory and Zariski geometries, and of the study of transcendental functions by model-theoretic methods.
Could the apparently continuous world of mathematics and physics be an approximation to a fundamentally finite universe? Boris Zilber explores this question through model theory, a branch of mathematics that studies theories and their models.
The lectures introduce the notion of global approximation: rather than viewing a finite model simply as a local discretisation of a continuous theory, one asks whether a single large finite structure can approximate an entire continuous structure globally. Zilber will describe how this perspective leads to compact complex structures and discuss its possible implications for spacetime and fundamental physics. Examples will include finite cyclic models of spacetime, Lorentz symmetry, quantum mechanics and string-theoretic structures. The lectures will also consider the distinction between the global mathematical structure and the local coordinates and measurements reconstructed by an observer.
Boris Zilber is Professor Emeritus of Mathematical Logic at the University of Oxford. His research is in model theory, geometry and their connections with other areas of mathematics and physics. He is one of the founders of geometric stability theory and Zariski geometries, and of the study of transcendental functions by model-theoretic methods.
Posted by: Yang-Hui He
Tue
29 Sep 2026
OPE = QNM: Analytic Structure, Black Holes, and Thermal Response
📍 London
Paolo Arnaudo
Abstract:
Thermal correlators admit two complementary descriptions. At short times they are controlled by local operator data through the thermal OPE, while at late times they are governed by collective excitations, or quasinormal modes. Underlying these two descriptions is a richer analytic structure: the continuation of thermal correlators to complex time can encode information about bulk causal structure and the black-hole interior through complex-time singularities. We show that the thermal OPE and the quasinormal-mode expansion overlap in a common domain of complex time and therefore constrain one another through analyticity. This relation can be used constructively in both directions. Starting from OPE data, we recover low-lying quasinormal modes by analytic continuation and determine large-overtone frequencies and residues from the singularity structure of the correlator. In Mellin space, the relation becomes a set of spectral sum rules connecting the OPE spectrum to QNM data and constraining the allowed spectral structure. I will illustrate these ideas for holographic thermal correlators, in particular scalar perturbations of the Schwarzschild-AdS_5 black brane. More broadly, this suggests a bootstrap perspective on real-time thermal response in which microscopic operator data, causality, collective spectra, and the analytic structure associated with black-hole geometry are treated as mutually constrained.
Thermal correlators admit two complementary descriptions. At short times they are controlled by local operator data through the thermal OPE, while at late times they are governed by collective excitations, or quasinormal modes. Underlying these two descriptions is a richer analytic structure: the continuation of thermal correlators to complex time can encode information about bulk causal structure and the black-hole interior through complex-time singularities. We show that the thermal OPE and the quasinormal-mode expansion overlap in a common domain of complex time and therefore constrain one another through analyticity. This relation can be used constructively in both directions. Starting from OPE data, we recover low-lying quasinormal modes by analytic continuation and determine large-overtone frequencies and residues from the singularity structure of the correlator. In Mellin space, the relation becomes a set of spectral sum rules connecting the OPE spectrum to QNM data and constraining the allowed spectral structure. I will illustrate these ideas for holographic thermal correlators, in particular scalar perturbations of the Schwarzschild-AdS_5 black brane. More broadly, this suggests a bootstrap perspective on real-time thermal response in which microscopic operator data, causality, collective spectra, and the analytic structure associated with black-hole geometry are treated as mutually constrained.
Posted by: Alan Rios Fukelman
Thu
24 Sep 2026
An Effective S-Matrix Approach to Black Hole Mergers
📍 London
Hyun Jeong
(Tokyo)
Abstract:
In this talk, I will propose an effective S-matrix framework for describing low-frequency gravitational waves from black hole mergers. Instead of starting from a Lagrangian and performing its derivative expansion, we directly expand the observable in the low-frequency regime within the KMOC formalism. Organizing this expansion with soft theorems at O(G^2), I will show how the logarithmic tail, the recoil, and the nonlinear memory emerge from the one-loop amplitude and the graviton cut contribution. Finally, I will identify the matching data needed to fully determine the low-frequency waveform.
Reference: arXiv:2609.10329
In this talk, I will propose an effective S-matrix framework for describing low-frequency gravitational waves from black hole mergers. Instead of starting from a Lagrangian and performing its derivative expansion, we directly expand the observable in the low-frequency regime within the KMOC formalism. Organizing this expansion with soft theorems at O(G^2), I will show how the logarithmic tail, the recoil, and the nonlinear memory emerge from the one-loop amplitude and the graviton cut contribution. Finally, I will identify the matching data needed to fully determine the low-frequency waveform.
Reference: arXiv:2609.10329
Posted by: Kymani Armstrong-Williams
Thu
17 Sep 2026
Deep-layered machines have a built-in Occam's razor
📍 London
Thomas Fink
(LIMS)
Abstract:
Many complex systems map vast numbers of microscopic descriptions onto far fewer macroscopic outcomes. Surprisingly, these input-output maps strongly favor simple outputs. We analyze an exactly solvable deep-layered Boolean machine and prove that increasing depth drives the distribution of the output \(F\) toward exponential decay in Kolmogorov complexity, \(P(F) \propto 2^{-K(F)}\), before ultimately collapsing onto the two constant functions. Our results show that hierarchical composition alone can generate an intrinsic Occam's razor, providing an analytical explanation for simplicity bias in learning and evolution.
Many complex systems map vast numbers of microscopic descriptions onto far fewer macroscopic outcomes. Surprisingly, these input-output maps strongly favor simple outputs. We analyze an exactly solvable deep-layered Boolean machine and prove that increasing depth drives the distribution of the output \(F\) toward exponential decay in Kolmogorov complexity, \(P(F) \propto 2^{-K(F)}\), before ultimately collapsing onto the two constant functions. Our results show that hierarchical composition alone can generate an intrinsic Occam's razor, providing an analytical explanation for simplicity bias in learning and evolution.
Posted by: Kymani Armstrong-Williams
Fri
4 Sep 2026
A menagerie of Euclidean constructions for 3D holographic cosmologies
📍 London
Alejandro Vilar López
(U. British Columbia)
Abstract:
In this talk, I will introduce a large family of solutions of Euclidean three-dimensional gravity coupled to heavy matter particles that, upon continuation to Lorentzian signature, contain a closed big-bang / big-crunch cosmology entangled with additional asymptotically AdS regions. The construction generalizes the one introduced by Antonini-Sasieta-Swingle (AS2), but the extra analytic control available in three dimensions makes it possible to embed more general cosmologies (e.g., approximately homogeneous and isotropic ones) in a relatively conventional AdS/CFT setup. I will then discuss to what extent these saddles containing a closed universe can dominate the path integral, introducing possible competing geometries, and comment on a general necessary condition for the dominance of the cosmological saddle points.
In this talk, I will introduce a large family of solutions of Euclidean three-dimensional gravity coupled to heavy matter particles that, upon continuation to Lorentzian signature, contain a closed big-bang / big-crunch cosmology entangled with additional asymptotically AdS regions. The construction generalizes the one introduced by Antonini-Sasieta-Swingle (AS2), but the extra analytic control available in three dimensions makes it possible to embed more general cosmologies (e.g., approximately homogeneous and isotropic ones) in a relatively conventional AdS/CFT setup. I will then discuss to what extent these saddles containing a closed universe can dominate the path integral, introducing possible competing geometries, and comment on a general necessary condition for the dominance of the cosmological saddle points.
Posted by: Martin Lagares
Thu
3 Sep 2026
Axions, Monopoles, and Gravity
📍 London
Yu Komiya
(Kyoto)
Abstract:
Phenomenological interest in axions originated from its potential to solve long-standing questions including the strong CP problem, their position as a candidate of dark matter, and their natural introduction through string compactifications. As several models appear to contain sequential symmetry breaking, the potential effects of axion theories on cosmology through their prediction of early universe defect formation gained it cosmological attention. These defects are expected to contain information about the theory’s vacuum structure, to link to the formation of primordial black holes, and to produce detectable signals through the catalysis of exotic processes. This talk reviews the modern intrigue of axion cosmology, and explores the unique effect of an axionic background on monopoles, which is thought to be able to form a stable state in flat space. The consequences of introducing gravitational effects to the system is then analysed; the talk summarises with a commentary on the diverse theoretical, phenomenological, cosmological, and astrophysical relevance of such a line of inquiry. Specifically, the UV extension of this topic through the moduli dynamics of the core monopole will be briefly discussed, which might allow a more complete consideration of stability, as well as relate to a more general understanding of defects through the UV link between quantum field theory and gravity.
Phenomenological interest in axions originated from its potential to solve long-standing questions including the strong CP problem, their position as a candidate of dark matter, and their natural introduction through string compactifications. As several models appear to contain sequential symmetry breaking, the potential effects of axion theories on cosmology through their prediction of early universe defect formation gained it cosmological attention. These defects are expected to contain information about the theory’s vacuum structure, to link to the formation of primordial black holes, and to produce detectable signals through the catalysis of exotic processes. This talk reviews the modern intrigue of axion cosmology, and explores the unique effect of an axionic background on monopoles, which is thought to be able to form a stable state in flat space. The consequences of introducing gravitational effects to the system is then analysed; the talk summarises with a commentary on the diverse theoretical, phenomenological, cosmological, and astrophysical relevance of such a line of inquiry. Specifically, the UV extension of this topic through the moduli dynamics of the core monopole will be briefly discussed, which might allow a more complete consideration of stability, as well as relate to a more general understanding of defects through the UV link between quantum field theory and gravity.
Posted by: Kymani Armstrong-Williams