Date/Time : 29 Apr 2026 15:00
Venue : S17 #04-06 (Seminar Room 1)
Speaker : Juncheng Wei, The Chinese University of Hong Kong

In 2023, one year before his death, H. Brezis posted 28 open questions which he described as “challenging and difficult”. In this talk I will give complete answer to the first open question—Problem 1.1 on Brezis-Nirenberg problem on three dimensional unit ball, and the seventh open question—Problem 3.1 on harmonic map equation on disk.

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Date/Time : 29 Apr 2026 15:00
Venue : S17 #04-04 (Seminar Room 3)
Speaker : Heejong Lee, Korea Institute for Advanced Study (KIAS)

Given a Galois representation attached to a regular algebraic cuspidal automorphic representation, the Hodge–Tate weight of the Galois representation is matched with the weight of the automorphic representation. Serre weight conjectures are mod p analogue of such a correspondence, relating ramification at p of a mod p Galois representation and Serre weights of mod p algebraic automorphic forms. In this talk, I will discuss how to understand Serre weight conjectures and modularity lifting as a relationship between representation theory of finite groups of Lie type (e.g. GSp4(Fp)) and the geometry of p-adic local Galois representations. Then I will explain the proof idea in the case of GSp4. This is based on a joint work with Daniel Le and Bao V. Le Hung.

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Date/Time : 22 Apr 2026 14:00
Venue : S17 #04-06 (Seminar Room 1)
Speaker : Jia Shi, Indiana University Bloomington

In this talk, I will introduce the implosion blow-up results for the compressible Euler, the compressible Navier-Stokes equations, and the defocusing nonlinear Schrödinger equation. We will discuss the existence of self-similar solutions and the stability near those solutions. During the talk, I will mention our work with Gonzalo Cao-Labora, Javier Gómez-Serrano, and Gigliola Staffilani on the first non-radial implosion result for those three equations. If there is time, I will also mention our work on self-similar solutions of a hydrodynamic equation that may formally arise as potential blow-up profiles of the focusing NLS equation.

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Date/Time : 22 Apr 2026 15:00
Venue : S17 #04-06 (Seminar Room 1)
Speaker : Khakim Egamberganov, National University of Singapore

We study the long-time behaviour of vorticity in three-dimensional axisymmetric Euler flows without swirl. This equation is globally well-posed when the initial vorticity satisfies some integrability conditions, but due to the presence of vortex stretching term, the vorticity and related quantities tend to grow in time. In this talk, we will discuss some improved upper and lower bounds for vorticity growth. This talk is based on joint work with Yao Yao.

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Date/Time : 22 Apr 2026 17:00
Venue : S17 #04-04 (Seminar Room 3)
Speaker : Phan Quoc Vuong,

Blow-up of a graph is a useful trick in extremal graph theory, replacing every vertex with a finite collection of copies so that the copies of two vertices are adjacent if and only if the originals are. In this talk, I will explain how to extend the blow-up trick to general combinatorial objects, and discuss about its potential application, illustrated by a recent result related to hypergraph Turan problem.

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Date/Time : 22 Apr 2026 16:00
Venue : S17 #04-04 (Seminar Room 3)
Speaker : Swee Hong Chan, Rutgers University

A sequence of nonnegative real numbers a_1, a_2,… , a_n, is log-concave if a_i^2 >= a_{i-1}a_{i+1} for all i ranging from 2 to n-1. Examples of log-concave inequalities range from inequalities that are readily provable, such as the binomial coefficients a_i = \binom{n}{i}, to intricate inequalities that have taken decades to resolve, such as the number of independent sets a_i in a matroid M with i elements (otherwise known as the first Mason’s conjecture; and was resolved by June Huh in 2010 in a remarkable breakthrough). It is then natural to ask if it can be shown that the latter type of inequalities is intrinsically more challenging than the former. In this talk, we provide a rigorous framework to answer this type of questions, by employing a combination of combinatorics, complexity theory, and geometry.

This is a joint work with Igor Pak.

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Date/Time : 21 Apr 2026 12:00
Venue : S17 #04-06 (Seminar Room 1)
Speaker : Ulrich Horst, Humboldt University, Berlin

We establish a simple microstructure foundation for rough log-normal volatility models such as the rough Bergomi model. Unlike in earlier microstructure model we do not assume that that market orders arrive according to a heavy-tailed Hawkes process. Instead, we assume that orders arrive according to a standard Poisson process but have long lasting impact on asset price volatility. After suitable scaling the logarithmic volatility converges weakly to fractional Brownian motion mit H<1/2. Weak convergence rates are also established. The talk is based on joint work with Paul Hager, Thomas Wagenhofer and Wei Xu.

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Date/Time : 17 Apr 2026 14:00
Venue : S17 #04-06 (Seminar Room 1)
Speaker : Joven Jia Xuan Teo, National University of Singapore

The nilpotent orbits of a Lie algebra are important objects relevant to representation theory, for instance in the definition of wavefront sets. If the algebra in question is one arising from a nondegenerate symmetric, symplectic, or Hermitian space over a topological field, it is known that the nilpotent orbits can be parametrised by objects called admissible labelled partitions. Furthermore, one can define in a reasonably simple way a partial ordering of these partitions that conjecturally corresponds to the closure ordering of the nilpotent orbits.

In this talk, we will introduce these admissible labelled partitions and the partial ordering defined on them. We then summarise the ideas in Djokovic’s proof of the real case. Finally, we discuss the obstacles in attempting to generalise these ideas to the p-adic case and beyond.

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Date/Time : 15 Apr 2026 16:30
Venue : S17 #05-11 (Seminar Room 5)
Speaker : Zhang Junyi, Nanyang Technological University

Quantum Approximate Optimization Algorithm (QAOA) was proposed as a variational quantum algorithm for solving combinatorial optimization problems. In this talk, I will discuss some recent observations in quantum circuit dynamics of QAOA. We identify three dynamical phases in the quantum circuits: 1) quasi-adiabatic phase, 2) quantum chaotic phase, and 3) shallow circuit phase. Particularly, we find that the quasi-adiabatic phase and the shallow circuit phase are separated by a dynamical quantum critical point indicated by the entanglement entropy. Moreover, the quantum chaotic phase emerges in digitized quantum circuit while absent for continuous unitary evolution. Our study calls for better understanding of quantum algorithms realized in quantum circuits.

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