Fri, 18 Jun 2021

Generalized entropy in topological string theory

Gabriel Wong
(Fudan University)

The holographic entanglement entropy formula identifies the generalized entropy of the bulk AdS spacetime with the entanglement entropy of the boundary CFT. However the bulk microstate interpretation of the generalized entropy remains poorly understood. Progress along this direction requires understanding how to define Hilbert space factorization and entanglement entropy in the bulk closed string theory.   As a toy model for AdS/CFT, we study the entanglement entropy of closed strings in the topological A model, which enjoys a gauge-string duality.   We define a notion of generalized entropy for closed strings on the resolved conifold using the replica trick.   As in AdS/CFT, we find this is dual to (defect) entanglement entropy in the dual Chern Simons gauge theory.   Our main result is a bulk microstate interpretation of generalized entropy in terms of open strings and their edge modes, which we identify as entanglement branes.   


More precisely, we give a self consistent factorization of the closed string Hilbert space which introduces open string edge modes transforming under a q-deformed surface symmetry group. Compatibility with this symmetry requires a q-deformed definition of entanglement entropy. Using the topological vertex formalism, we define the Hartle Hawking state for the resolved conifold and compute its q-deformed entropy directly from the reduced density matrix.   We show that this is the same as the generalized entropy.   Finally, we relate non local aspects of our factorization map to analogous phenomenon recently found in JT gravity.

Tue, 15 Jun 2021

Harish-Chandra Lefschetz principle for branching laws of general linear groups

Kei Yuen Chan
(Fudan University)

The Harish-Chandra Lefschetz principle asserts representation theory for real groups, p-adic groups and automorphic forms should be placed on an equal footing. A particular example in this aspect is that Ciubotaru and Trapa constructed Arakawa-Suzuki type functors between category of Harish-Chandra modules and category of graded Hecke algebra modules, giving an explicit connection on the representation categories between p-adic and real sides. 

This talk plans to begin with comparing the representation theory between real and p-adic general linear groups, such as unitary and unipotent representations. Then I shall explain results in more details on the p-adic branching law from GL(n+1) to GL(n), including branching laws for Arthur type representations (one of the non-tempered Gan-Gross-Prasad conjectures). The analogous results and predictions on the real group side will also be discussed. Time permitting, I will explain a notion of left-right Bernstein-Zelevinsky derivatives and its applications on branching laws.

Thu, 30 Apr 2020

Fields of finite dp-rank

Will Johnson
(Fudan University)

The classification of NIP fields is a major open problem in model theory.  This talk will be an overview of an ongoing attempt to classify NIP fields of finite dp-rank.  Let $K$ be an NIP field that is neither finite nor separably closed.  Conjecturally, $K$ admits exactly one definable, valuation-type field topology (V-topology).  By work of Anscombe, Halevi, Hasson, Jahnke, and others, this conjecture implies a full classification of NIP fields.  We will sketch how this technique was used to classify fields of dp-rank 1, and what goes wrong in higher ranks.  At present, there are two main results generalizing the rank 1 case.  First, if $K$ is an NIP field of positive characteristic (and any rank), then $K$ admits at most one definable V-topology.  Second, if $K$ is an unstable NIP field of finite dp-rank (and any characteristic), then $K$ admits at least one definable V-topology.  These statements combine to yield the classification of positive characteristic fields of finite dp-rank. In characteristic 0, things go awry in a surprising way, and it becomes necessary to study a new class of "finite rank" field topologies, generalizing V-topologies.  The talk will include background information on V-topologies, NIP fields, and dp-rank.

Mon, 14 Jan 2019

16:00 - 17:00

On boundary value problem for steady Navier-Stokes system in 2D exterior domains

Mikhail Korobkov
(Fudan University)

We study solutions to stationary Navier-Stokes system in two dimensional exterior domains, namely, existence of these solutions and their asymptotical behavior. The talk is based on the recent joint papers with K. Pileckas and R. Russo where the uniform boundedness and uniform convergence at infinity for arbitrary solution with finite Dirichlet integral were established. Here  no restrictions on smallness of fluxes are assumed, etc.  In the proofs we develop the ideas of the classical papers of Gilbarg & H.F. Weinberger (Ann. Scuola Norm.Pisa 1978) and Amick (Acta Math. 1988).

Tue, 10 May 2016

Coupled second order evolution equations with memory effects and variable sign kernels

Kun-Peng Jin
(Fudan University)

We consider a system of coupled second order integro-differential evolution equations in a Hilbert space, which is partially damped through memory effects. A global existence theorem regarding the solutions to its Cauchy problem is given, only under basic conditions that the memory kernels possess positive definite primitives but without nonnegative/decreasing assumptions. Following this, we find an approach to successfully obtain the stability of the system energy and various decay rates. Moreover, the abstract results are applied to several concrete systems in the real world, including the Timoshenko type. This is a joint work with Professor Ti-Jun Xiao (Fudan University) and Professor Jin Liang (Shanghai Jiaotong University)

Mon, 28 Jan 2008
Oxford-Man Institute

The Feynman-Kac formula and related problems

Prof. Jiangang Ying
(Fudan University)
This talk gives a survey on a series of work which I and co-authors have been doing for 10 years. I will start from the Feynman-Kac type formula for Dirichlet forms. Then a necessary and sufficient condition is given to characterize the killing transform of Markov processes. Lastly we shall discuss the regular subspaces of linear transform and answer some problems related to the Feynman-Kac formula
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