13:00

### SUPERTRANSLATIONS, ANGULAR MOMENTUM, AND COVARIANCE IN 4D ASYMPTOTICALLY FLAT SPACE

## Abstract

Forthcoming events in this series

Tue, 11 Jun 2024

13:00

13:00

TBA

Massimo Porrati

(NYU)

I will present a supertranslation-invariant and Lorentz-covariant definition of angular momentum in asymptotically flat 4D spacetime. This definition uses only asymptotic metric data and reproduces the flux necessary to obtain known radiation reaction effects. The formula has an appealing physical interpretation, it extends to Lorentz boost charges and integrated fluxes, and agrees with other existing definitions in appropriate reference frames.

Tue, 28 May 2024

13:00

13:00

L2

Andrew Lucas

(Boulder )

In this talk I will describe the systematic construction of strongly interacting RG fixed points with a finite disorder strength. Such random-field disorder is quite common in condensed matter experiment, necessitating an understanding of the effects of this disorder on the properties of such fixed points. In the past, such disordered fixed points were accessed using e.g. epsilon expansions in perturbative quantum field theory, using the replica method to treat disorder. I will show that holography gives an alternative picture for RG flows towards disordered fixed points. In holography, spatially inhomogeneous disorder corresponds to inhomogeneous boundary conditions for an asymptotically-AdS spacetime, and the RG flow of the disorder strength is captured by the solution to the Einstein-matter equations. Using this construction, we have found analytically-controlled RG fixed points with a finite disorder strength. Our construction accounts for, and explains, subtle non-perturbative geometric effects that had previously been missed. Our predictions are consistent with conformal perturbation theory when studying disordered holographic CFTs, but the method generalizes and gives new models of disordered metallic quantum criticality.

Tue, 21 May 2024

13:00

13:00

L2

George Papadopoulos

(King's College London)

I shall review some aspects of the relationship between scale and conformal invariance in 2-dimensional sigma models. Then, I shall explain how such an investigation is related to the Perelman's ideas of proving the Poincare' conjecture. Using this, I shall demonstrate that scale invariant sigma models with B-field coupling and compact target space are conformally invariant. Several examples will also be presented that elucidate the results. The talk is based on the arXiv paper 2404.19526.

Tue, 14 May 2024

13:00

13:00

L2

Gabriel Wong

(Oxford )

One of the major insights gained from holographic duality is the relation between the physics of black holes and quantum chaotic systems. This relation is made precise in the duality between two dimensional JT gravity and random matrix theory. In this work, we generalize this to a duality between AdS3 gravity and a random ensemble of approximate CFT's. The latter is described by a combined tensor and matrix model, describing the OPE coefficients and spectrum of a theory that approximately satisfies the bootstrap constraints. We show that the Feynman diagrams of the random ensemble produce a sum over 3 manifolds that agrees with the partition function of 3d gravity. A crucial element of this dictionary is the Virasoro TQFT, which defines the bulk gravitational path integral via the cutting and sewing relations of topological field theory. Time permitting, we will explain why this TQFT has gravitational edge modes degrees of freedom whose entanglement gives rise to gravitational entropy.

Tue, 07 May 2024

13:00

13:00

L2

Andrea Antinucci

(SISSA)

The progress in our understanding of symmetries in QFT has led to the proposal that the complete information on a symmetry structure is encoded in a TQFT in one dimension higher, known as the Symmetry TFT. This picture is well understood for finite symmetries, and I will explain the extension to continuous symmetries in the first part of the talk, based on a paper with F. Benini. This extension requires studying new TQFTs with a non-compact spectrum of operators. Like for finite symmetries, these TQFTs capture anomalies and topological manipulations via their topological boundary conditions. The main new ingredient for continuous symmetries is dynamical gauging, which is described by maps between different TQFTs. I will use this to derive the Symmetry TFT for the non-invertible chiral symmetry of QED. Moreover, the various TQFTs related by dynamical gauging arise as different boundary conditions of a unique TQFT in two dimensions higher. In the second part of the talk, based on work in progress with F. Benini and G. Rizi, I will use these tools to derive some new connections between the Symmetry TFTs and the universal EFTs describing the spontaneous symmetry breaking of any (generalized) global symmetry.

Tue, 30 Apr 2024

13:00

13:00

L2

Frank Coronado

(McGill)

Self-dual Yang-Mills famously have a description in terms of twistors; one of the outstanding questions is how to promote it to full (non-self-dual) Yang-Mills and learn about its dynamics. In this talk, I will present some progress in this direction in the "most symmetric" Yang-Mills theory; namely N=4 super Yang-Mills in four dimensions. I will express the full Yang-Mills theory as a deformation of self-dual Yang-Mills. By treating the deformation perturbatively and using the formalism of twistors, I will write down the loop-integrands of correlation functions of determinant operators in the planar limit at any order in the 't Hooft coupling. Interestingly, the final expression is given by a partition function of a "dual" matrix model. This in turn manifests a ten-dimensional structure that combines spacetime and R-charge symmetries of SYM.

Tue, 23 Apr 2024

13:00

13:00

L2

Shu-Heng Shao

(Stony Brook University)

In massless QED, we find that the classical U(1) chiral symmetry is not completely broken by the Adler-Bell-Jackiw anomaly. Rather, it is resurrected as a generalized global symmetry labeled by the rational numbers. Intuitively, this new global symmetry in QED is a composition of the naive axial rotation and a fractional quantum Hall state. The conserved symmetry operators do not obey a group multiplication law, but a non-invertible fusion algebra. We further generalize our construction to QCD, and show that the neutral pion decay can be derived from a matching condition of the non-invertible global symmetry.

Tue, 05 Mar 2024

13:00

13:00

L3

Herman Verlinde

(Princeton)

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

12:30

L4

Andrew Rolph

(Vrije U., Brussels)

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

12:30

L4

Dionysios Anninos

(King's College London)

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

12:30

L4

Akshay Yelleshpur Srikant

(Oxford )

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

12:30

L4

Balint Koczor

(Oxford )

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

12:30

L4

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

13:00

L3

Faroogh Moosavian

(Oxford)

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

13:00

L2

Xinan Zhou

(Beijing)

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

13:00

L1

Cyril Closset

(Birmingham)

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

13:00

L1

Matthew Yu

(Oxford )

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

13:00

L1

Romain Ruzziconi

(Oxford)

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

13:00

L1

Gabriel Wong

(Oxford)

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

13:00

L1

Julius Grimminger

(Oxford )

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

13:00

L1

Christian Copetti

(Oxford)

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

13:00

L1

Sourav Sarkar

(Uppsala)

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

13:00

L1

Alessandro Mininno

(DESY)

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.

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.

My results are based on arXiv:2203.16550 [hep-th], arXiv:2208.11130 [hep-th] and arXiv:2303.16216 [hep-th].

Mon, 19 Jun 2023

13:00

13:00

L3

Sebastian Mizera

(IAS)

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

17:15

L3

Sebastian Mizera

(IAS)

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.

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