2024 SEUYC Theoretical Physics Seminars -- Upcoming

Apr. 23rd (Tues.), 2024

Congkao Wen

Abstract

In this talk, I will discuss some exact results of four-point correlation functions in N=4 super Yang-Mills. I will focus on the correlator involving two determinant operators (often called giant gravitons) and two superconformal primary operators in the stress tensor multiplet, and study the associated integrated correlator by integrating over the spacetime dependence. I will show that the integrated correlator can be reformulated as an infinite sum of protected three-point functions, which leads to exact expressions of the integrated correlator in the planar limit and beyond. The SL(2, Z) completion of the results and the comparison with string theory will be discussed as well.

Apr. 16th (Tues.), 2024

Carlos Nunez 

(Swansea University)

Abstract

I will present recent advances in the duality between gauge fields and strings. In particular I will focus on holographic dual to field theories with a UV-conformal point and confining IR dynamics with large number of colours and flavours. The presentation is planned to be pedagogical, avoiding many technical details, trying to convey the main idea. The talk is based on the papers I published in the last five months and work in progress

Apr. 11th (Thurs.), 2024

Rongxin Miao

(Sun Yat-sen University)

Abstract

This talk discusses the Casimir effect of a wedge and its holographic dual. We prove that the wedge Casimir effect is universally determined by the displacement operator in smooth limit. Besides, we argue that the wedge Casimir energy increases with the opening angle. Furthermore, we construct the holographic dual of wedges in AdS/BCFT in general dimensions. We verify that our proposal can produce the correct smooth limit. Next, we discuss the wedge contribution to holographic entanglement entropy and find it increases with the opening angle, similar to the wedge Casimir energy. Finally, we conclude with some open questions.

Apr. 9th (Tues.), 2024

Shota Komatsu

(CERN, Switzerland)

Abstract

We study analytical properties and integrable structures of the meson spectrum in large Nc QCD2. We show that the integral equation that determines the masses of the mesons, often called the ’t Hooft equation, is equivalent to finding solutions to a TQ-Baxter equation. Using the Baxter equation, we extract systematic expansions of the energy levels as well as analytic asymptotic expressions for wavefunctions. Our analysis extends previous results for a special quark mass by Fateev et al. to arbitrary quark masses. This reformulation, together with its relation to an inhomogeneous Fredholm equation, is particularly suited for analytical treatments and makes accessible the analytic structure of the spectrum in the complex plane of the quark masses. We also  comment on applications of our techniques to non-perturbative topological string partition functions.

Mar. 26th (Tues.), 2024

Abstract

This presentation focuses on the lattice and matrix bootstrap methods, distinguished by their utilization of the equation of motion as bootstrap constraints. These methods share key characteristics with the closely related fields of quantum mechanics bootstrap and many-body bootstrap. The presentation will cover the application of the bootstrap method to the matrix model theory, with a particular emphasis on the ground state of BFSS. Additionally, I will discuss the latest results in bootstrap finite N matrix model theory, including the upcoming bootstrap result of SU(2) lattice gauge theory.

Mar. 21st (Thur.), 2024

Bartek Czech

(IAS, Tsinghua University)

Abstract

An important class of quantum states are those whose entanglement entropies can be computed by minimal cuts through some bulk structure---a holographic spacetime or a random tensor network. Such states obey linear constraints on their entanglement entropies, which are known as holographic entropy inequalities. I present two new infinite families of holographic entropy inequalities. The entropies featured in these inequalities are best visualized on graphs whose incidence relations reflect subsystem inclusion. These graphs turn out to be tessellations of the torus and the real projective plane. The non-contractible cycles on these manifolds play an indispensable role in proving the inequalities, which shows that they hold for essentially topological reasons. Physically, the inequalities represent constraints on holographic error correcting codes and, in some cases, the entropy of two-sided black holes. If time allows it, I will sketch bonus applications, which involve a non-planar polytope called cubohemioctahedron and (more speculatively) the toric code.

Mar. 19th (Tues.), 2024

Sameer Murthy

(King's College London, UK)

Abstract

The fundamental heterotic string has a tower of BPS states with an exponential growth in the charges. The fate of these BPS states at strong coupling is an old, much-debated topic: do they become a black hole or a string gas? I will discuss a new approach to this problem, i.e. the gravitational path integral corresponding to the supersymmetric index of these states. I will show that the saddle-point configuration of this path integral is a supersymmetric rotating non-extremal Euclidean black hole. This configuration is singular in the two-derivative theory but is resolved by higher-derivative terms from string theory. Remarkably, the one-loop, four-derivative F-term contribution to the prepotential leads to a precise match of the gravitational and microscopic index. Thus, the nature of the BPS string at strong coupling depends on the precise observable being probed. The thermal states transition to a winding condensate and a gas of strings without ever reaching a small black hole, while the index is captured by the rotating Euclidean black hole solution, is constant, and thus smoothly connected to the microscopic ensemble.

Mar. 12th (Tues.), 2024

Alexey S. Koshelev

(ShanghaiTech University)

Abstract

In my talk I will explain how infinite derivatives naturally arise in consideration of quantum properties of general gravity theories. I will construct the most general propagator around Minkowski and (anti)-de Sitter backgrounds proving that an infinite tower of derivatives is inevitable in order to exorcise ghosts. Then I will show that this construction has a direct relation to strings, especially to string field theory. I will elaborate on the issue of ghosts and on a connection with a recent idea of stubs in QFT and SFT.

Mar. 5th (Tues.), 2024

16:00-17:00

Bethe ansatz in 2d conformal field theory

Slides.pdf

Abstract

The usual approach to study 2d CFT relies on the Virasoro algebra and its representation theory. Moving away from the criticality, this infinite dimensional symmetry is lost so it is useful to have a look at 2d CFTs from more general framework of quantum integrability. Every 2d conformal field theory has a natural infinite dimensional family of commuting higher spin Hamiltonians that can be constructed out of Virasoro generators. Perhaps surprisingly two different sets of Bethe ansatz equations are known that be used to diagonalize these (one by Bazhanov-Lukyanov-Zamolodchikov and another by Litvinov). I want to discuss these constructions as well as their relation to W algebras and the affine Yangian symmetry.

Feb. 27th (Tues.), 2024

16:00-17:00

Matthias Gaberdiel

Abstract

The symmetric orbifold of T^4, Sym_N(T4), is dual to tensionless string theory on AdS3 x S3 x T4 with one unit of NS-NS flux. In this talk I will study the deformation of the symmetric orbifold theory that corresponds to switching on R-R flux (and hence the string tension) in the bulk string theory. Working in the planar large N limit as well as the limit of large charge, I will explain how the deformed symmetric orbifold theory can be explicitly solved in terms of what appears to be an integrable system. Among other things, this allows us to give explicit predictions about the anomalous conformal dimensions of all multi-magnon states.

Jan. 16th (Tues.), 2024

16:00-17:00

(CERN, Switzerland)

Abstract

Lorentzian correlators of local operators exhibit surprising singularities in theories with gravity duals. These are associated with null geodesics in an emergent bulk geometry. I will talk about singularities of the thermal response function dual to propagation of waves on the AdS Schwarzschild black hole background. I will present the analytic form of the leading singularity dual to a bulk geodesic that winds around the black hole. Remarkably, it exhibits a boundary group velocity larger than the speed of light, whose dual is the angular velocity of null geodesics at the photon sphere. The strength of this singularity is controlled by the classical Lyapunov exponent associated with the instability of nearly bound photon orbits.