Forthcoming events in this series


Mon, 15 Feb 2021
12:45
Virtual

TBA

Simeon Hellerman
(Kavli IPMU)
Mon, 08 Feb 2021
12:45
Virtual

Confinement in 4d N=1 from 6d N=(2,0)

Lakshya Bhardwaj
(University of Oxford)
Abstract

We will discuss confinement in 4d N=1 theories obtained after soft supersymmetry breaking deformations of 4d N=2 Class S theories. Confinement is characterised by a subgroup of the 1-form symmetry group of the theory that is left unbroken in a massive vacuum of the theory. The 1-form symmetry group is encoded in the Gaiotto curve associated to the Class S theory, and its spontaneous breaking in a vacuum is encoded in the N=1 curve (which plays the role of Seiberg-Witten curve for N=1) associated to that vacuum. Using this proposal, we will recover the expected properties of confinement in N=1 SYM theories, and the theories studied by Cachazo, Douglas, Seiberg and Witten. We will also recover the dependence of confinement on the choice of gauge group and discrete theta parameters in these theories.

Mon, 01 Feb 2021
12:15
Virtual

5D non-Lorentzian CFT’s and 6D Physics

Neil Lambert
(King's College London)
Abstract

NOTE: unusual time! 

 

We discuss a class of 5-dimensional supersymmetric non-Lorentzian Lagrangians with an SU(1,3) conformal symmetry. These theories arise from reduction of 6-dimensional CFT's on a comformally compactified spacetime. We use the SU(1,3) Ward identities to find the form of the correlation functions which have a rich structure. Furthermore we show how these can be used to reconstruct  6-dimensional  CFT correlators. 
 

Mon, 25 Jan 2021
12:45
Virtual

Moduli Space Holography and the Finiteness of Flux Vacua

Thomas Grimm
(Utrecht)
Abstract

In this talk I describe a holographic perspective to study field spaces that arise in string compactifications. The constructions are motivated by a general description of the asymptotic, near-boundary regions in complex structure moduli spaces of Calabi-Yau manifolds using Hodge theory. For real two-dimensional field spaces, I introduce an auxiliary bulk theory and describe aspects of an associated sl(2) boundary theory. The classical bulk reconstruction is provided by the sl(2)-orbit theorem, which is a famous and general result in Hodge theory. I then apply this correspondence to the flux landscape of Calabi-Yau fourfold compactifications and discuss how this allows us to prove that the number of self-dual flux vacua is finite. I will point out how the finiteness result for supersymmetric fluxes relates to the Hodge conjecture.

Mon, 18 Jan 2021
14:00
Virtual

Ensemble averaging torus orbifolds

Nathan Benjamin
(Princeton)
Abstract

 We generalize the recent holographic correspondence between an ensemble average of free bosons in two dimensions, and a Chern-Simons-like theory of gravity in three dimensions, by Afkhami-Jeddi et al and Maloney and Witten. We find that the correspondence also works for toroidal orbifolds, but we run into difficulties generalizing to K3 and Calabi-Yau sigma models. For the case of toroidal orbifolds, we extend the holographic correspondence to averages of correlation functions of twist operators by using properties of rational tangles in three-dimensional balls and their covering spaces. Based on work to appear with C. Keller, H. Ooguri, and I. Zadeh. 

Mon, 30 Nov 2020
12:45
Virtual

Twisted QFT and Operator Algebra

Jihwan Oh
(University of Oxford)
Abstract

I will discuss various operator algebras in supersymmetric quantum field theories in various dimensions. The operator algebras are induced and classified by generalised topological twists. Omega deformation plays an important role in connecting different sectors. This talk is based on previous works and a work in progress with Junya Yagi.

Mon, 23 Nov 2020
12:45
Virtual

An optical theorem for CFT and high-energy string scattering in AdS at one loop

Tobias Hansen
(University of Oxford)
Abstract

In this talk I will present an optical theorem for perturbative CFTs, which directly computes the double discontinuity of CFT correlators in terms of the discontinuities of correlators at lower loops or lower points, in analogy to the optical theoreom for scattering amplitudes. I will then discuss the application of this theorem to high-energy scattering of type IIb strings in AdS at one loop and finite 't Hooft coupling. Tidal excitations are taken into account and shown to be efficiently described by an AdS vertex function. The result is related to the 1987 flat space result of Amati, Ciafaloni and Veneziano via the flat space limit in impact parameter space.

Mon, 16 Nov 2020
12:45
Virtual

Geometry, Strings and QFTs in d > 4

Lakshya Bhardwaj
(University of Oxford)
Abstract

We will discuss recent progress in understanding (ordinary and generalized) symmetries, dualities and classification of superconformal field theories in 5d and 6d, which involves the study of M-theory and F-theory compactified on Calabi-Yau threefolds.

Mon, 09 Nov 2020
12:45
Virtual

Classical scattering of spinning black holes from quantum amplitudes

Alexander Ochirov
(University of Oxford)
Abstract

In view of the recent observations of gravitational-wave signals from black-hole mergers, classical black-hole scattering has received considerable interest due to its relation to the classical bound-state problem of two black holes inspiraling onto each other. In this talk I will discuss the link between classical scattering of spinning black holes and quantum scattering amplitudes for massive spin-s particles. Considering the first post-Minkowskian (PM) order, I will explain how the spin-exponentiated structure of the relevant tree-level amplitude follows from minimal coupling to Einstein's gravity and in the s → ∞ limit generates the black holes' complete series of spin-induced multipoles. The resulting scattering function will be shown to encode in a simple way the classical net changes in the black-hole momenta and spins at 1PM order and to all orders in spins. I will then comment on the results and challenges at 2PM order and beyond.
 

Mon, 02 Nov 2020
12:45
Virtual

Instantons, symmetries and anomalies in five dimensions

Pietro Benetti Genolini
(University of Cambridge)
Abstract

All five-dimensional non-abelian gauge theories have a U(1)U(1)I​U(1) global symmetry associated with instantonic particles. I will describe a mixed ’t Hooft anomaly between this and other global symmetries of  the theory, namely the one-form center symmetry or ordinary flavor symmetry for theories with fundamental matter. I will explore some general dynamical properties of the candidate phases implied by the anomaly, and apply our results to supersymmetric gauge theories in five dimensions, analysing the symmetry enhancement patterns occurring at their conjectured RG fixed points.

Mon, 26 Oct 2020
12:45
Virtual

Discrete and higher-form symmetries from wrapped M5-branes

Federico Bonetti
(University of Oxford)
Abstract

A vast class of 4d SCFTs can be engineered by wrapping a stack of M5-branes on a Riemann surface. These SCFTs can exhibit a variety of global symmetries, continuous or discrete, including both ordinary (0-form) symmetries, as well as generalized (higher-form) symmetries. In this talk, I will focus on discrete and higher-form symmetries in setups with M5-branes on a smooth Riemann surface. Adopting a holographic point of view, a crucial role is played by topological mass terms in 5d supergravity (similar to BF terms in four dimensions). I will discuss how the global symmetries of the boundary 4d theory are inferred from the 5d topological terms, and how one can compute 4d ‘t Hooft anomalies involving discrete and/or higher-form symmetries.

Mon, 19 Oct 2020
12:45
Virtual

Joint Moments of Characteristic Polynomials of Random Unitary Matrices

Jon Keating
(University of Oxford)
Abstract

 I will review what is known and not known about the joint moments of the characteristic polynomials of random unitary matrices and their derivatives. I will then explain some recent results which relate the joint moments to an interesting class of measures, known as Hua-Pickrell measures. This leads to the proof of a conjecture, due to Chris Hughes in 2000, concerning the asymptotics of the joint moments, as well as establishing a connection between the measures in question and one of the Painlevé equations.

Mon, 12 Oct 2020
12:45
Virtual

Scattering Equations in AdS

Lorenz Eberhard
(IAS)
Abstract

I will discuss an analogue of the CHY formalism in AdS. Considering the biadjoint scalar theory on AdS, I will explain how to rewrite all the tree-level amplitudes as an integral over the moduli space of punctured Riemann spheres. Contrary to the flat space, the scattering equations are operator-valued. The resulting formula is motivated via a bosonic ambitwistor string on AdS and can be proven to be equivalent to the corresponding Witten diagram computation by applying a series of contour deformations.

Mon, 15 Jun 2020
12:45
Virtual

SQCD and pairs of pants --- ZOOM SEMINAR

Shlomo Razamat
(Technion)
Abstract

We will show that minimally supersymmetric SU(N+2) SQCD models in the middle of the conformal window can be engineered by compactifying certain 6d SCFTs on three punctured spheres. The geometric construction of the 4d theories predicts numerous interesting strong coupling effects, such as IR symmetry enhancements and duality. We will discuss this interplay between simple geometric and group theoretic considerations and complicated field theoretic strong coupling phenomena. For example, one of the dualities arising geometrically from different pair-of-pants decompositions of a four punctured sphere  is an $SU(N+2)$ generalization of the Intriligator-Pouliot duality of $SU(2)$ SQCD with $N_f=4$, which is a degenerate, $N=0$, instance of our discussion. 

Mon, 08 Jun 2020
12:45
Virtual

Branes and the Swampland -- ZOOM SEMINAR

Hee-Cheol Kim
(POSTECH Pohang)
Abstract

I will talk about a novel idea on the Swampland program that uses consistency of what lives on the string probes in gravitational theories. The central charges and the levels of current algebras of 2d CFTs on these strings can be calculated by anomaly inflow mechanism and used to provide constraints on the supergravity theories based on unitarity of the worldsheet CFT. I will show some of the theories with 8 or 16 supersymmetries, which are otherwise consistent looking, belong to the Swampland.

Mon, 25 May 2020
12:45
Virtual

Symplectic duality and implosion -- ZOOM SEMINAR

Andrew Dancer
(University of Oxford)
Abstract

We discuss hyperkahler implosion spaces, their relevance to group actions and why they should fit into the symplectic duality picture. For certain groups we present candidates for the symplectic duals of the associated implosion spaces and provide computational evidence. This is joint work with Amihay Hanany and Frances Kirwan.
 

Mon, 18 May 2020
12:45
Virtual

Compensating strong coupling with large charge -- ZOOM SEMINAR

Susanne Reffert
(Bern)
Abstract

Over the last few years, it has become clear that working in sectors of large global charge leads to significant simplifications when studying strongly coupled CFTs. It allows us in particular to calculate the CFT data as an expansion in inverse powers of the large charge.
In this talk, I will introduce the large-charge expansion via the simple example of the O(2) model and will then apply it to a number of other systems which display a richer structure, such as non-Abelian global symmetry groups.
 

Mon, 11 May 2020
12:45
Virtual

Holomorphic anomaly in Vafa-Witten theory -- ZOOM SEMINAR

Pavel Putrov
(ICTP Trieste)
Abstract

Vafa-Witten theory is a topologically twisted version of 4d N=4 super Yang-Mills theory. In my talk I will tell how to derive a holomorphic anomaly equation for its partition function on a Kaehler 4-manifold with b_2^+=1 and b_1=0 from the path integral of the effective theory on the Coulomb branch. I will also briefly mention an alternative and somewhat similar computation of the same holomorphic anomaly in the effective 2d theory obtained by compactification of the corresponding 6d (2,0) theory on the 4-manifold.
 

Mon, 04 May 2020
12:45
Virtual

Superstrings, Calabi-Yau Manifolds and Machine-Learning -- ZOOM SEMINAR

Yang-Hui He
(City University)
Abstract

We review how historically the problem of string phenomenology lead theoretical physics first to algebraic/diffenretial geometry, and then to computational geometry, and now to data science and AI.
With the concrete playground of the Calabi-Yau landscape, accumulated by the collaboration of physicists, mathematicians and computer scientists over the last 4 decades, we show how the latest techniques in machine-learning can help explore problems of physical and mathematical interest.
 

Mon, 27 Apr 2020
15:00

Decomposition of 2d theories with 1-form symmetries

Eric Sharpe -- ZOOM SEMINAR
(Virginia Tech)
Abstract

In this talk, we will discuss two-dimensional theories with discrete

one-form symmetries, examples (which we have been studying

since 2005), their properties, and gauging of the one-form symmetry.

Their most important property is that such theories decompose into a

disjoint union of theories, recently deemed `universes.'

This decomposition has the effect of restricting allowed nonperturbative

sectors, in a fashion one might deem a `multiverse interference effect,'

which has had applications in topics including Gromov-Witten theory and

gauged linear sigma model phases.  After reviewing one-form symmetries

and decomposition in general, we will discuss a particular 

example in detail to explicitly illustrate these properties and 

to demonstrate how

gauging the one-form symmetry projects onto summands in the

decomposition.  If time permits, we will briefly review

analogous phenomena in four-dimensional theories with three-form symmetries,

as recently studied by Tanizaki and Unsal.

Mon, 09 Mar 2020
12:45
L3

Bottom-up construction of 4d N=2 SCFTs

Carlo Meneghelli
(Oxford)
Abstract

In this talk, I will argue how the observation that four-dimensional N=2 superconformal field theories are interconnected via the operation of Higgsing can be turned into an effective method to construct such SCFTs. A fundamental role is played by the (generalized) free field realization of the associated VOAs.

Mon, 02 Mar 2020
12:45

Aspects of gauge-strings duality

Carlos Nunez
(Swansea)
Abstract

I will discuss recently published examples of SCFTs in
two dimensions and their dual backgrounds. Aspects of the
integrability of these string backgrounds will be described in
correspondence with those of the dual SCFTs. The comparison with four and
six dimensional examples will be presented. It time allows, the case of
conformal quantum mechanics will also be addressed.