Forthcoming events in this series


Tue, 11 Mar 2025
13:00
L5

Topological Quantum Dark Matter via Standard Model's Global Gravitational Anomaly Cancellation

Juven Wang
(LIMS)
Abstract
In this talk, we propose that topological order can replace sterile neutrinos as dark matter candidates 
to cancel the Standard Model’s global gravitational anomalies. Standard Model (SM) with 15 Weyl fermions per family 
(lacking the 16th, the sterile right-handed neutrino νR) suffers from mixed gauge-gravitational anomalies tied to baryon number plus or minus
lepton number B±L symmetry. Including νR per family can cancel these anomalies, but when B±L
symmetry is preserved as discrete finite subgroups rather than a continuous U(1), the perturbative
local anomalies become nonperturbative global anomalies. We systematically enumerate
these gauge-gravitational global anomalies involving discrete B ± L that are enhanced from the
fermion parity ZF2 to ZF2N , with N = 2, 3, 4, 6, 9, etc. The discreteness of B ± L is constrained by
multi-fermion deformations beyond-the-SM and the family number Nf . Unlike the free quadratic
νR Majorana mass gap preserving the minimal ZF2 , we explore novel scenarios canceling (B ± L)-gravitational anomalies 
while preserving the ZF2N discrete symmetries, featuring 4-dimensional interacting gapped topological orders 
or gapless sectors (e.g., conformal field theories). We propose symmetric anomalous sectors as 
quantum dark matter to cancel SM’s global anomalies. We find the uniqueness
of the family number at Nf = 3, such that when the representation of ZF2N from the faithful B + L
for baryons at N = Nf = 3 is extended to the faithful Q + NcL for quarks at N = NcNf = 9, this
symmetry extension ZNc=3 → ZNcNf =9 → ZNf =3 matches with the topological order dark matter
construction. Key implications include: (1) a 5th force mediating between SM and dark matter via
discrete B±L gauge fields, (2) dark matter as topological order quantum matter with gapped anyon
excitations at ends of extended defects, and (3) Ultra Unification and topological leptogenesis.
Tue, 04 Mar 2025
13:00
L6

Irrelevant Perturbations in 1+1D Integrable Quantum Field Theory

Olalla Castro Alvaredo
(City St George's, University of London)
Abstract

In this talk I will review recent results on the development of a form factor program for integrable quantum field theories (IQFTs) perturbed by irrelevant operators. It has been known for a long time that under such perturbations integrability is preserved and that the two-body scattering phase gets deformed in a simple manner. The consequences of such a deformation are stark, leading to theories that exhibit a so-called Hagedorn transition and no UV completion. These phenomena manifest physically in several distinct ways. In our work we have mainly asked the question of how the deformation of the S-matrix translates into the correlation functions of the deformed theory. Does the scaling of correlators at long and short distances capture any of the "pathologies" mentioned above? Can our understanding of irrelevant perturbations tell us something about the space of IQFTs and about their form factors? In this talk I will answer these questions in the afirmative, summarising work in collaboration with Stefano Negro, Fabio Sailis and István M. Szécsényi.

Tue, 25 Feb 2025
13:00
L5

Bootstrapping the 3d Ising Stress Tensor

Petr Kravchuk
(KCL)
Abstract

I will discuss the recent progress in the numerical bootstrap of the 3d Ising CFT using the correlation functions of stress-energy tensor and the relevant scalars. This numerical bootstrap setup gives excellent results which are two orders of magnitude more accurate than the previous world's best. However, it also presents many significant technical challenges. Therefore, in addition to describing in detail the numerical results of this work, I will also explain the state-of-the art numerical bootstrap methods that made this study possible. Based on arXiv:2411.15300 and work in progress.

Tue, 18 Feb 2025
13:00
L5

Homotopy algebras, quantum field theory and AKSZ-gravity

Leron Borsten
(University of Hertfordshire)
Abstract

We’ll begin by introducing homotopy algebras (assuming no background) and their intimate connection to quantum field theory, with a briefly summary of some applications: scattering amplitude recursion relations, colour-kinematics duality, and generalised asymptotic observables. We’ll then introduce (deformed) Alexandrov–Kontsevich–Schwarz–Zaboronsky theories as the paradigmatic example of this framework, before developing their applications to gravity in two, three and four dimensions.   

Tue, 11 Feb 2025
13:00
L5

Generalized gauging in 2+1d lattice models

Kansei Inamura
(Oxford)
Abstract

Gauging is a systematic way to construct a model with non-invertible symmetry from a model with ordinary group-like symmetry. In 2+1d dimensions or higher, one can generalize the standard gauging procedure by stacking a symmetry-enriched topological order before gauging the symmetry. This generalized gauging procedure allows us to realize a large class of non-invertible symmetries. In this talk, I will describe the generalized gauging of finite group symmetries in 2+1d lattice models. This talk will be based on my ongoing work with L. Bhardwaj, S.-J. Huang, S. Schäfer-Nameki, and A. Tiwari.

Tue, 04 Feb 2025
13:00
L5

Symmetries of Coupled Minimal Models

Connor Behan
(ITP Sao Paolo)
Abstract

When tensor products of N minimal models accumulate at central charge N, they also admit relevant operators arbitrarily close to marginality. This raises the tantalizing possibility that they can be use to reach purely Virasoro symmetric CFTs where the breaking of extended chiral symmetry can be seen in a controlled way. This talk will give an overview of the theories where this appears to be the case, according to a brute force check at low lying spins. We will also encounter an interesting non-example where the same type of analysis can be used to give a simpler proof of integrability.

Tue, 28 Jan 2025
13:00
L5

Symmetric impurities and constraints on their screening

Christian Copetti
(Oxford )
Abstract

"The question of whether an impurity can be screened by bulk degrees of freedom is central to the study of defects and to (variations of) the Kondo problem. In this talk I discuss how symmetry, generalized or not, can give serious constraints on the possible scenarios at long distances. These can be quantified in the UV where the defect is weakly coupled. I will give some examples of interesting symmetric defect RG flows in (1+1) and (2+1)d.

Based on https://arxiv.org/pdf/2412.18652 and work in progress."

Tue, 21 Jan 2025
13:00
L5

Celestial Holography and Self-Dual Einstein Gravity

David Skinner
Abstract

Celestial Holography posits the existence of a holographic description of gravitational theories in asymptotically flat space-times. To date, top-down constructions of such dualities involve a combination of twisted holography and twistor theory. The gravitational theory is the closed string B model living in a suitable twistor space, while the dual is a chiral 2d gauge theory living on a stack of D1 branes wrapping a twistor line. I’ll talk about a variant of these models that yields a theory of self-dual Einstein gravity (via the Plebanski equations) in four dimensions. This is based on work in progress with Roland Bittleston, Kevin Costello & Atul Sharma.

Tue, 03 Dec 2024
13:00
L2

Quantized axial charge of lattice fermions and the chiral anomaly

Arkya Chatterje
(MIT )
Abstract

Realizing chiral global symmetries on a finite lattice is a long-standing challenge in lattice gauge theory, with potential implications for non-perturbative regularization of the Standard Model. One of the simplest examples of such a symmetry is the axial U(1) symmetry of the 1+1d massless Dirac fermion field theory: it acts by equal and opposite phase rotations on the left- and right-moving Weyl components of the Dirac field. This field theory also has a vector U(1) symmetry which acts identically on left- and right-movers. The two U(1) symmetries exhibit a mixed anomaly, known as the chiral anomaly. In this talk, we will discuss how both symmetries are realized as ordinary U(1) symmetries of an "ultra-local" lattice Hamiltonian, on a finite-dimensional Hilbert space. Intriguingly, the anomaly of the Abelian U(1) symmetries in the infrared (IR) field theory is matched on the lattice by a non-Abelian Lie algebra. The lattice symmetry forces the low-energy phase to be gapless, closely paralleling the effects of the anomaly in the field theory.

Tue, 26 Nov 2024
13:00
L2

Late time saturation of the Einstein-Rosen bridge dual to the Double Scaled SYK model

Vijay Balasubramanian
(UPenn and Oxford)
Abstract

In this talk I will explain how the size of the Einstein-Rosen (ER) bridge dual to the Double Scaled SYK (DSSYK) model saturates at late times because of finiteness of the underlying quantum Hilbert space.  I will extend recent work implying that the ER bridge size equals the spread complexity of the dual DSSYK theory with an appropriate initial state.  This work shows that the auxiliary "chord basis'' used to solve the DSSYK theory is the physical Krylov basis of the spreading quantum state.  The ER bridge saturation follows from the vanishing of the Lanczos spectrum, derived by methods from Random Matrix Theory (RMT).

Tue, 19 Nov 2024
13:00
L2

Symmetry topological field theory and generalised Kramers–Wannier dualities

Clement Delcamp
(IHES)
Abstract

A modern perspective on symmetry in quantum theories identifies the topological invariance of a symmetry operator within correlation functions as its defining property. Within this paradigm, a framework has emerged enabling a calculus of topological defects in terms of a higher-dimensional topological quantum field theory. In this seminar, I will discuss aspects of this construction for Euclidean lattice field theories. Exploiting this framework, I will present generalisations of the celebrated Kramers-Wannier duality of the Ising model, as combinations of gauging procedures and generalised Fourier transforms of the local weights encoding the dynamics. If time permits, I will discuss implications of this framework for the real-space renormalisation group flow of these theories.

Tue, 12 Nov 2024
13:00
L2

Machine Learning and Calabi-Yau Manifolds

Magdalena Larfors
(Uppsala)
Abstract

: With motivation from string compactifications, I will present work on the use of machine learning methods for the computation of geometric and topological properties of Calabi-Yau manifolds.

Thu, 07 Nov 2024
14:00
N3.12

SPECIAL STRING THEORY SEMINAR: An infrared on-shell action in asymptotically flat spacetimes

Ana-Maria Raclariu
(KCL)
Abstract

 One of the main entries in the AdS/CFT dictionary is a relation between the bulk on-shell partition function with specified boundary conditions and the generating function of correlation functions of primary operators in the boundary CFT. In this talk, I will show how to construct a similar relation for gravity in 4d asymptotically flat spacetimes. For simplicity, we will restrict to the leading infrared sector, where a careful treatment of soft modes and their canonical partners leads to a non-vanishing on-shell action. I will show that this action localizes to a codimension-2 surface and coincides with the generating function of 2d CFT correlators involving insertions of Kac-Moody currents. The latter were previously shown, using effective field theory methods, to reproduce the leading soft graviton theorems in 4d. I will conclude with comments on the implications of these results for the computation of soft charge fluctuations in the vacuum. 

Tue, 05 Nov 2024
13:00
L2

Optimal transport, Ricci curvature, and gravity compactifications

Andrea Mondino
(Oxford )
Abstract

In the talk, I will start by recalling some basics of optimal transport and how it can be used to define Ricci curvature lower bounds for singular spaces, in a synthetic sense. Then, I will present some joint work with De Luca-De Ponti and Tomasiello,  where we show that some singular spaces,  naturally showing up in gravity compactifications (namely, Dp-branes),  enter the aforementioned setting of non-smooth spaces satisfying Ricci curvature lower bounds in a synthetic sense.  Time permitting, I will discuss some applications to the Kaluza-Klein spectrum.

Tue, 29 Oct 2024
13:00
L2

Fivebrane Stars

Yoav Zigdon
(Cambridge )
Abstract
The low energy limit of string theory contains solutions of large redshift, either near an event horizon or extended objects. Alday, de Boer, and Messamah compared the massless BTZ black hole to the ensemble average of horizonless BPS solutions with the same charges and found them to differ. I will show that averaging gives rise to a spherically symmetric and horizon-free "fivebrane star" solution by employing an effective string description for Type IIA NS5-branes. By further including internal excitations of the extended objects in this description, we obtain solutions of smaller sizes and greater redshifts relative to those with purely transverse excitations, thereby approaching the black hole phase.


 

Tue, 22 Oct 2024
13:00
L2

Heterotic islands

Ida Zadeh
(Southampton)
Abstract

In this talk I will discuss asymmetric orbifolds and will focus on their application to toroidal compactifications of heterotic string theory. I will consider theories in 6 and 4 dimensions with 16 supercharges and reduced rank. I will present a novel formalism, based on the Leech lattice, to construct ‘islands’ without vector multiplets.

Tue, 15 Oct 2024
13:00
L2

Mirror Symmetry and Level-rank Duality for 3d N=4 Rank 0 SCFTs

Niklas Garner
(Oxford )
Abstract

Three-dimensional QFTs with 8 supercharges (N=4 supersymmetry) are a rich playground rife with connections to mathematics. For example, they admit two topological twists and furnish a three-dimensional analogue of the famous mirror symmetry of two-dimensional N=(2,2) QFTs, creatively called 3d mirror symmetry, that exchanges these twists. Recently, there has been increased interest in so-called rank 0 theories that typically do not admit Lagrangian descriptions with manifest N=4 supersymmetry, but their topological twists are expected to realize finite, semisimple TQFTs which are amenable to familiar descriptions in terms of, e.g., modular tensor categories and/or rational vertex operator algebras. In this talk, based off of joint work (arXiv:2406.00138) with Thomas Creutzig and Heeyeon Kim, I will introduce two families of rank 0 theories exchanged by 3d mirror symmetry and various mathematical conjectures stemming from our analysis thereof.

Tue, 17 Sep 2024
13:00
L1

TBA

Vija Balasubramanian
(UPenn)
Tue, 11 Jun 2024
13:00
TBA

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

Massimo Porrati
(NYU)
Abstract
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
L2

Disordered quantum critical fixed points from holography

Andrew Lucas
(Boulder )
Abstract

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
L2

Scale and conformal invariance in 2-dimensional sigma models

George Papadopoulos
(King's College London)
Abstract

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
L2

3d gravity from an ensemble of approximate CFTs

Gabriel Wong
(Oxford )
Abstract

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
L2

Continuous symmetries, non-compact TQFTs, and holography

Andrea Antinucci
(SISSA)
Abstract

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
L2

Determinants in self-dual N = 4 SYM and twistor space

Frank Coronado
(McGill)
Abstract
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
L2

What's done cannot be undone: non-invertible symmetries

Shu-Heng Shao
(Stony Brook University)
Abstract

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.