Forthcoming events in this series


Tue, 05 Mar 2024
13:00
L3

Double scaled SYK and the quantum geometry of 3D de Sitter space

Herman Verlinde
(Princeton)
Abstract

In this talk, I describe an exact duality between the double scaling limit of the SYK model and quantum geometry of de Sitter spacetime in three dimensions. The duality maps the so-called chord rules that specify the exact SYK correlations functions to the skein relations that govern the topological interactions between world-line operators in 3D de Sitter gravity.

This talk is part of the series of Willis Lamb Lectures in Theoretical Physics. Herman Verlinde is the Lamb Lecturer of 2024.

Tue, 27 Feb 2024
12:30
L4

Page curves and replica wormholes from chaotic dynamics

Andrew Rolph
(Vrije U., Brussels)
Abstract

What is the bare minimum needed to get a unitarity-consistent black hole radiation entropy curve? In this talk, I will show how to capture both Hawking's non-unitary entropy curve, and density matrix-connecting contributions that restore unitarity, in a toy quantum system with chaotic dynamics. The motivation is to find the simplest possible dynamical model, dropping all superfluous details, that captures this aspect of gravitational physics. In the model, the Hamiltonian obeys random matrix statistics within microcanonical windows, the entropy of the averaged state gives the non-unitary curve, the averaged entropy gives the unitary curve, and the difference comes from matrix index contractions in the Haar averaging that connect the density matrices in a replica wormhole-like manner.

Tue, 20 Feb 2024
12:30
L4

Gravitational Observatories

Dionysios Anninos
(King's College London)
Abstract

We discuss timelike surfaces of finite size in general relativity and the initial boundary value problem. We consider obstructions with the standard Dirichlet problem, and conformal version with improved properties. The ensuing dynamical features are discussed with general cosmological constant.

Tue, 13 Feb 2024
12:30
L4

Scattering amplitudes and Celestial Holography

Akshay Yelleshpur Srikant
(Oxford )
Abstract

The S-Matrix in flat space is a naturally holographic observable. S-Matrix elements thus contain valuable information about the putative dual CFT. In this talk, I will first introduce some basic aspects of Celestial Holography and then explain how these can be inferred directly from scattering amplitudes. I will then focus on how the singularity structure of amplitudes interplays with traditional CFT structures particularly in the context of the operator product expansion (OPE) of the dual CFT. I will conclude with some discussion about the role played by supersymmetry in simplifying the putative dual CFT.
 

Tue, 06 Feb 2024
12:30
L4

Will (near-term) quantum computers deliver real advantage?

Balint Koczor
(Oxford )
Abstract
Quantum computers are becoming a reality and current generations of machines are already well beyond the 50-qubit frontier. However, hardware imperfections still overwhelm these devices and it is generally believed the fault-tolerant, error-corrected systems will not be within reach in the near term: a single logical qubit needs to be encoded into potentially thousands of physical qubits which is prohibitive.
 
Due to limited resources, in the near term, we need to resort to quantum error mitigation techniques. I will explain the basic concepts and then discuss my results on exponentially effective error mitigation [PRX 11, 031057 (2021), PRX Quantum, accepted (2024)], including an architecture of multiple quantum processors that perform the same quantum computation in parallel [PR Applied 18, 044064 (2022)]; using their outputs to verify each other results in an exponential suppression of errors.
 

I will then explain that hybrid quantum-classical protocols are the most promising candidates for achieving early quantum advantage. These have the potential to solve real-world problems---including optimisation or ground-state search---but they suffer from a large number of circuit repetitions required to extract information from the quantum state. I will explain some of our recent results as hybrid quantum algorithms that exploit so-called classical shadows (random unitary protocols) in order to extract and post-process a large amount of information from the quantum computer [PRX 12, 041022 (2022)] and [arXiv:2212.11036]. I will finally identify the most likely areas where quantum computers may deliver a true advantage in the near term.

Tue, 30 Jan 2024
12:30
L4

Towards the large-charge sector of the critical O(N) model with an interface defect

Vito Pellizzani
(Bern)
Further Information

In conformal field theories, special classes of operators, such as defects and local operators carrying large quantum numbers, have received a lot of attention in recent years. In this talk, I will present some work in progress regarding the extraction of CFT data in the critical O(N) model with a codimension-one flat defect (interface), paying special attention to the case where local operators in large traceless symmetric representations of O(N) (the so-called 'large-charge operators' in this context) are inserted in the bulk. The talk will include a discussion of certain general features of codimension-one defect CFTs, a small review of the large-charge bootstrap, as well as an overview of the current understanding of the phase diagram of the boundary/interface critical O(N) model.

Tue, 23 Jan 2024
13:00
L3

The Bethe-Gauge Correspondence for Superspin Chains

Faroogh Moosavian
(Oxford)
Abstract

The Bethe-Gauge Correspondence (BGC) of Nekrasov and Shatashvili, linking quantum integrable spin chains to two-dimensional supersymmetric gauge theories with N=2 supersymmetry, stands out as a significant instance of the deep connection between supersymmetric gauge theories and integrable models. In this talk, I will delve into this correspondence and its origins for superspin chains. To achieve this, I will first elucidate the Bethe Side and its corresponding Gauge Side of the BGC. Subsequently, it becomes evident that the BGC can be naturally realized within String Theory. I will initially outline the brane configuration for the realization of the Gauge Side. Through the use of string dualities, this brane configuration will be mapped to another, embodying the Bethe Side of the correspondence. The 4D Chern-Simons theory plays a crucial role in this latter duality frame, elucidating the integrability of the Bethe Side. Lastly, I will elaborate on computing the main object of interest for integrable superspin chains—the R-matrix—from the BGC. While this provides a rather comprehensive picture of the correspondence, some important questions remain for further clarification. I will summarize some of the most interesting ones at the end of the talk.


 

Tue, 16 Jan 2024
13:00
L2

Defect two-point functions in 6d (2,0) theories

Xinan Zhou
(Beijing)
Abstract

In this talk, I will discuss correlation functions in 6d (2, 0) theories of two 1/2-BPS operators inserted away from a 1/2-BPS surface defect. In the large central charge limit the leading connected contribution corresponds to sums of tree-level Witten diagram in AdS7×S4 in the presence of an AdS3 defect. I will show that these correlators can be uniquely determined by imposing only superconformal symmetry and consistency conditions, eschewing the details of the complicated effective Lagrangian. I will present the explicit result of all such two-point functions, which exhibits remarkable hidden simplicity.

Tue, 28 Nov 2023
13:00
L1

Global structures of SQFTs from rank-one Seiberg-Witten geometries

Cyril Closset
(Birmingham)
Abstract

 I will explore subtle aspects of rank-one 4d N=2 supersymmetric QFTs through their low-energy Coulomb-branch physics. This low-energy Lagrangian is famously encoded in the Seiberg-Witten (SW) curve, which is a one-parameter family of elliptic curves. Less widely appreciated is the fact that various properties of the QFTs, including properties that cannot be read off from the Lagrangian, are nonetheless encoded into the SW curve, in particular in its Mordell-Weil group. This includes the global form of the flavour group, the one-form symmetries under which defect lines are charged, and the "global form" of the theory. In particular, I will discuss in detail the difference between the pure SU(2) and the pure SO(3) N=2 SYM theories from this perspective. I will also comment on 5d SCFTs compactified on a circle in this context.

Tue, 21 Nov 2023
13:00
L1

KLT for windings strings and nonrelativistic string theory

Matthew Yu
(Oxford )
Abstract

I will discuss a KLT relation of closed string amplitudes into open string amplitudes for closed string states carrying winding and momentum in toroidal compactifications. The goal is to introduce an interesting D-brane set up in the target space in order to accommodate both quantum numbers of the closed string. I will then discuss KLT factorization of amplitudes for winding closed strings in the presence of a critical Kalb-Ramond field and the relevance of this work for nonrelativistic string theory when taking the zero Regge limit. 

Tue, 14 Nov 2023
13:00
L1

Carrollian perspective on celestial holography

Romain Ruzziconi
(Oxford)
Abstract

I will review some aspects of gravity in asymptotically flat spacetime and mention important challenges to obtain a holographic description in this framework. I will then present two important approaches towards flat space holography, namely Carrollian and celestial holography, and explain how they are related to each other. Similarities and differences between flat and anti-de Sitter spacetimes will be emphasized throughout the talk. 
 

Tue, 07 Nov 2023
13:00
L1

3D gravity, Virasoro TQFT, and ensembles of approximate CFT’s

Gabriel Wong
(Oxford)
Abstract

Recent progress in AdS/CFT has provided a good understanding of how the bulk spacetime is encoded in the entanglement structure of the boundary CFT. However, little is known about how spacetime emerges directly from the bulk quantum theory. We address this question in AdS3 pure gravity, which we formulate as a topological quantum field theory. We explain how gravitational entropy can be viewed as bulk entanglement entropy of gravitational edge modes.  These edge modes transform under a quantum group symmetry. This suggests an effective description of bulk microstates in terms of collective, anyonic degrees of freedom whose entanglement leads to the emergence of the bulk spacetime.  Time permitting we will discuss a proposal for how our bulk TQFT arises from an ensemble of approximate CFT’s, generalizing the relation between JT gravity and random matrix ensemble.

Tue, 31 Oct 2023
13:00
L1

Theories with 8 Supercharges, the Higgs Mechanism, and Symplectic Singularities

Julius Grimminger
(Oxford )
Abstract

I will talk about supersymmetric quantum field theories with 8 supercharges in dimensions 3-6. After a brief introduction I will mostly speak about the moduli space of vacua of such theories, and in particular their Higgs branches, which are so called symplectic singularities (or mild generalisations thereof). Powerful theorems from mathematics say that a singular Higgs branch is stratified into a disjoint union of smooth open subsets, so called symplectic leaves. This stratification matches exactly the pattern of partial Higgsings of the theory in question. After introducing the stratification and explaining its physical interpretation, I will show how brane systems and so called magnetic quivers can be used to compute it.

Tue, 24 Oct 2023
13:00
L1

Duality defects, anomalies and RG flows

Christian Copetti
(Oxford)
Abstract

We review the construction of non-invertible duality defects in various dimensions. We explain how they can be preserved along RG flows and how their realization on gapped phases contains their 't Hooft anomalies. We finally give a presentation of the anomalies from the Symmetry TFT. Time permitting I will discuss some possible future applications.

Tue, 17 Oct 2023
13:00
L1

An exact solution to cosmological bootstrap using 6j symbols

Sourav Sarkar
(Uppsala)
Abstract

We shall consider a crossing equation of the Euclidean conformal group in terms of conformal partial waves and in particular, a position independent representation of this equation. We shall briefly discuss the relevance of this equation to the problem of cosmological bootstrap. Thereafter, we shall sketch the derivation of the Biedenharn-Eliiot identity (a pentagon identity) for the 6j symbols of the conformal group and show how this provides us with an exact solution to said crossing equation. For the conformal group (which is non-compact), this involves some careful bookkeeping of the spinning representations. Finally, we shall discuss some consistency checks on the result obtained, and some open questions. 

Tue, 10 Oct 2023
13:00
L1

Generalized Symmetries in Argyres-Douglas Theories

Alessandro Mininno
(DESY)
Abstract
In this talk, I will discuss the dynamical consequences of having 1-form, 2-group and non-invertible symmetries in Argyres-Douglas (AD) theories.
I will first review how to construct (G,G') and D_p(G) theories from geometric engineering. Then, I will briefly introduce how 1-form symmetries are found in these AD theories, focusing on their dynamical consequences in the study of the Higgs branch for such theories.  Analogously, I will show how certain D_p(G) theories enjoy a 2-group structure due to a non-trivial extension between a discrete 1-form symmetry and a continuous 0-form symmetry, emphasizing the dynamical consequences that a 2-group structure entails, and the family of AD theories that have it. This analysis allowed us to "bootstrap" families of D_p(G) theories sharing the same properties. Finally, I discuss the presence of non-invertible symmetries in AD theories obtained by gauging the flavor symmetry of multiple D_p(SU(N)) theories. 

 

Mon, 19 Jun 2023
13:00
L3

Evaluating one-loop string amplitudes

Sebastian Mizera
(IAS)
Abstract

Scattering amplitudes in string theory are written as formal integrals of correlations functions over the moduli space of punctured Riemann surfaces. It's well-known, albeit not often emphasized, that this prescription is only approximately correct because of the ambiguities in defining the integration domain. In this talk, we propose a resolution of this problem for one-loop open-string amplitudes and present their first evaluation at finite energy and scattering angle. Our method involves a deformation of the integration contour over the modular parameter to a fractal contour introduced by Rademacher in the context of analytic number theory. This procedure leads to explicit and practical formulas for the one-loop planar and non-planar type-I superstring four-point amplitudes, amenable to numerical evaluation. We plot the amplitudes as a function of the Mandelstam invariants and directly verify long-standing conjectures about their behavior at high energies.

Mon, 12 Jun 2023
17:15
L3

Evaluating one-loop string amplitudes

Sebastian Mizera
(IAS)
Abstract

Scattering amplitudes in string theory are written as formal integrals of correlations functions over the moduli space of punctured Riemann surfaces. It's well-known, albeit not often emphasized, that this prescription is only approximately correct because of the ambiguities in defining the integration domain. In this talk, we propose a resolution of this problem for one-loop open-string amplitudes and present their first evaluation at finite energy and scattering angle. Our method involves a deformation of the integration contour over the modular parameter to a fractal contour introduced by Rademacher in the context of analytic number theory. This procedure leads to explicit and practical formulas for the one-loop planar and non-planar type-I superstring four-point amplitudes, amenable to numerical evaluation. We plot the amplitudes as a function of the Mandelstam invariants and directly verify long-standing conjectures about their behavior at high energies.

Mon, 12 Jun 2023
14:15
L1

Holographic description of code CFTs

Anatoly Dymarsky
(Kentucky)
Abstract

Recently, a relation was introduced connecting codes of various types with the space of abelian (Narain) 2d CFTs. We extend this relation to provide holographic description of code CFTs in terms of abelian Chern-Simons theory in the bulk. For codes over the alphabet Z_p corresponding bulk theory is, schematically, U(1)_p times U(1)_{-p} where p stands for the level. Furthermore, CFT partition function averaged over all code theories for the codes of a given type is holographically given by the Chern-Simons partition function summed over all possible 3d geometries. This provides an explicit and controllable example of holographic correspondence where a finite ensemble of CFTs is dual to "topological/CS gravity" in the bulk. The parameter p controls the size of the ensemble and "how topological" the bulk theory is. Say, for p=1 any given Narain CFT is described holographically in terms of U(1)_1^n times U(1)_{-1}^n Chern-Simons, which does not distinguish between different 3d geometries (and hence can be evaluated on any of them). When p approaches infinity, the ensemble of code theories covers the whole Narain moduli space with the bulk theory becoming "U(1)-gravity" proposed by Maloney-Witten and Afkhami-Jeddi et al.

Mon, 12 Jun 2023
13:00
L1

Spacetime and Duality symmetries

Peter West
(KCL )
Abstract

We argue that the existence of solitons in theories in which local symmetries are spontaneously broken requires spacetime to be enlarged by additional coordinates that are associated with large local transformations. In the context of gravity theories the usual coordinates of spacetime can be thought of arising in this way. E theory automatically contains such an enlarged spacetime. We propose that spacetime appears in an underlying theory when the local symmetries are spontaneously broken.

Mon, 05 Jun 2023
13:00
L1

Gravity’s Attractive Blocks

Seyed Morteza Hosseini
(Imperial College )
Abstract

There has been recent advances in understanding the microscopic origin of the Bekenstein-Hawking entropy of supersymmetric ant de Sitter (AdS) black holes using holography and localization applied to the dual quantum field theory. In this talk, after a brief overview of the general picture, I will propose a BPS partition function -- based on gluing elementary objects called gravitational blocks -- for known AdS black holes with arbitrary rotation and generic magnetic and electric charges. I will then show that the attractor equations and the Bekenstein-Hawking entropy can be obtained from an extremization principle.

Mon, 29 May 2023
13:00
L1

Operator dynamics in Floquet many-body systems

Takato Yoshimura
(All Souls. Oxford Physics)
Abstract

Random unitary circuits (RUCs) have served as important sources of insights in studying operator dynamics. While the simplicity of RUCs allows us to understand the nature of operator growth in a quantitative way, randomness of the dynamics in time prevents them to capture certain aspects of operator dynamics. To explore these aspects, in this talk, I consider the operator dynamics of a minimal Floquet many-body circuit whose time-evolution operator is fixed at each time step. In particular, I compute the partial spectral form factor of the model and show that it displays nontrivial universal physics due to operator dynamics. I then discuss the out-of-ordered correlator of the system, which turns out to capture the main feature of it in a generic chaotic many-body system, even in the infinite on-site Hilbert space dimension limit.

Mon, 22 May 2023
13:00
L1

Generalized Charges of Symmetries

Lakshya Bhardwaj
(Oxford)
Abstract

I will discuss various possible ways a global symmetry can act on operators in a quantum field theory. The possible actions on q-dimensional operators are referred to as q-charges of the symmetry. Crucially, there exist generalized higher-charges already for an ordinary global symmetry described by a group G. The usual charges are 0-charges, describing the action of the symmetry group G on point-like local operators, which are well-known to correspond to representations of G. We find that there is a neat generalization of this fact to higher-charges: i.e. q-charges are (q+1)-representations of G. I will also discuss q-charges for generalized global symmetries, including not only invertible higher-form and higher-group symmetries, but also non-invertible categorical symmetries. This talk is based on a recent (arXiv: 2304.02660) and upcoming works with Sakura Schafer-Nameki.

Mon, 15 May 2023
13:00
L1

From Poisson’s Ratio to Cosmology

Chris Herzog
(KCL )
Abstract

I will discuss how to place conformal boundary conditions on free higher derivative theories of scalars and spinors as well as the zoo of boundary renormalization group flows that connect the different boundary conditions.  Historically, there are connections to Poisson’s ratio and classical equations governing the bending of thin steel plates.  As these higher derivative theories are often invoked in the context of cosmology, there may be cosmological applications for the boundary conditions discussed here.
 

Mon, 08 May 2023
13:00
L1

Star-shaped quivers in four dimensions

Shlomo Razamat
(Technion)
Abstract
We will review the notion of across dimension IR dualities. As a concrete example we will  discuss such 4d across dimensions dual Lagrangian descriptions of compactifications of the 6d  minimal D type conformal matter theory on a sphere with arbitrary number of punctures. The Lagrangian has the form of a ``star shaped quiver'' with the rank of the central node depending on the 6d theory and the number and type of punctures. Using these Lagrangians one can construct across dimensions duals for arbitrary compactifications (any genus and type of punctures) of the D type conformal matter.