**2024年丘成桐中心理论物理研讨会**

**Upcoming Seminars in 2024**

| Name | Title |

August, 2024 16:00-17:00 | Jin Chen | TBA |

TBA |

We organize theoretical physics seminars regularly. The seminars are broadcasted online mostly by Zoom (sometimes in other methods). Interested people are free to join without registration in advance.

**The Zoom info is**

** URL:** https://us02web.zoom.us/j/3854420225?pwd=SXY4eWJKOTBFZWJDaE16aXpTamY1QT09

** Meeting ID:** 385 442 0225

** Passcode:** yauc

and China Standard Time (UTC+8) is used.

If you wish to give a talk, please write to any one of the faculty members. For other workshops, contact the organizers for the details.

Seminar information can also be found on the website of our Theoretical Physics Group at YCSEU. Events (yaucseu.github.io)

** Past Seminars in 2024**

Date | Name | Title |

June 18th (Tues.), 2024 16:00-17:00 (Offline and online) | Jun Nian (University of Chinese Academy of Sciences) | The Quantum Perspectives of Kerr Black Hole Formation and Evaporation |

Black holes are fascinating objects in nature. Although they are introduced as classical solutions in general relativity, their intrinsic nature should be quantum, which manifests during the black hole formation and evaporation processes. If string theory is claimed to be a quantum gravity candidate, it should be able to provide a consistent picture and elucidate some perspectives for black hole formation and evaporation. In this talk, we will focus on rotating Kerr black holes. On the one hand, we will show through a toy model that Kerr black holes can emerge naturally from the Virasoro minimal string theory. On the other hand, we use a field-theoretic approach to compute the time evolution of entanglement entropy between an evaporating Kerr black hole and its Hawking quanta, i.e., the Page curve, which provides a new resolution to the long-standing black hole information paradox. This talk is based on my recent papers, 2312.14287 and 2210.06762, and some work in progress. | ||

May 21st (Tues.), 2024 16:00-17:00 | Hjalte Frellesvig (Niels Bohr Institute, Denmark) | Feynman Integrals, Intersection Theory, and other Ideas |

Feynman integrals are the main mathematical building block of high precision contributions to scattering amplitudes in quantum field theories. In this talk I will discuss my work on these fascinating objects, such as their connection to the mathematical field of intersection theory, the geometric structures that may appear as integration surfaces, and the integrals that appear in expressions for Higgs production in the Standard Model. | ||

May 14th (Tues.), 2024
| Scott Collier (MIT) | 3d quantum gravity and Virasoro TQFT |

I will discuss the quantization of one of the simplest theories of gravity, three-dimensional Einstein gravity with negative cosmological constant. In particular I will describe a precise reformulation of AdS_3 quantum gravity in terms of a novel topological quantum field theory based on the quantization of the Teichmuller space of Riemann surfaces that we refer to as Virasoro TQFT. This proposal clarifies the relationship between pure AdS_3 quantum gravity and (two copies of) SL(2,R) Chern-Simons theory, and resolves some well-known issues with this lore. I will argue that moreover this proposal provides a practical framework for the computation of 3d gravity partition functions, and will describe how it elucidates various aspects of the holographic dual. | ||

Apr. 30th (Tues.), 2024 16:00-17:00 | Fabio Apruzzi (University of Padua, INFN, Italy) | Aspects of (non-)invertible symmetries from branes: symmetry theories and generalized charges |

Recently it has been observed that the string theory branes in geometric engineering and holography have a striking connection with generalized global symmetries. I will explain how branes, in a certain topological limit, not only furnish the symmetry generators, but also encode the so-called Symmetry Topological Field Theory (or SymTFT). For a d-dimensional quantum field theory (QFT), this is a (d+1)-dimensional topological field theory, whose topological defects encode both the symmetry generators (invertible or non-invertible) and the generalized charges. After having introduced the general setup, I will exemplify this for QFT with finite generalized (non-)invertible symmetries. Finally, I will discuss this prescription to non-finite symmetries. In particular, I will discuss the symmetry theory (SymTh) for non-invertible symmetries with transformation parameters in Q/Z, which are the ones that also appear in 4d particle physics. | ||

Apr. 23rd (Tues.), 2024 16:00-17:00 | Congkao Wen (Queen Marry University of London) | Exact results and modularity of giant graviton four-point correlator |

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 16:00-17:00 | Carlos Nunez (Swansea University) | Aspects of gauge-strings duality |

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 16:00-17:00 | Rongxin Miao (Sun Yat-sen University) | Casimir effect and holographic dual of wedges |

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 16:00-17:00 | Shota Komatsu (CERN, Switzerland) | 2d QCD and Integrability |

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 20:00-21:00 | Zechuan Zheng (Perimeter institute, Canada) | Revisiting Lattice and Matrix Bootstrap |

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 14:00-15:00 (Offline) | Bartek Czech (IAS, Tsinghua University) | Everything Everywhere All at Once: Holographic Entropy Inequalities, the Topology of Error Correction, Black Holes, Cubohemioctahedron, and (maybe) the Toric Code |

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 20:00-21:00 | Sameer Murthy (King's College London, UK) | Gravitational index of the heterotic string |

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 16:00-17:00 | Alexey S. Koshelev (ShanghaiTech University) | Infinite derivative gravity, String Field Theory and stubs |

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 | Tomáš Procházka (Institute of Physics, Czech Academy of Sciences) | Bethe ansatz in 2d conformal field theory |

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 (ETH Zurich, Switzerland) | Integrability in the symmetric orbifold |

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 | ## Alexander Zhiboedov(CERN, Switzerland) | Black hole bulk-cone singularities |

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. |

**Past Seminars in 2023**

Please refer to the following webpage:

Shing-Tung Yau Center Theoretical Physics Seminars in 2023(seu.edu.cn)

**Past Seminars in 2022**

Please refer to the following webpage:

Shing-Tung Yau Center Theoretical Physics Seminars in 2022 (seu.edu.cn)