Tue, 04 Feb 2025
13:00
L5

Symmetries of Coupled Minimal Models

Connor Behan
(ITP Sao Paolo)
Abstract

When tensor products of N minimal models accumulate at central charge N, they also admit relevant operators arbitrarily close to marginality. This raises the tantalizing possibility that they can be use to reach purely Virasoro symmetric CFTs where the breaking of extended chiral symmetry can be seen in a controlled way. This talk will give an overview of the theories where this appears to be the case, according to a brute force check at low lying spins. We will also encounter an interesting non-example where the same type of analysis can be used to give a simpler proof of integrability.

Tue, 11 Mar 2025
15:30
L4

Quiver with potential and attractor invariants

Pierre Descombes
(Imperial College London)
Abstract
Given a quiver (a directed graph) with a potential (a linear combination of cycles), one can study moduli spaces of the associated noncommutative algebra and associate so-called BPS invariants to them. These are interesting because they have a deep link with cluster algebras and provide some kind of noncommutative analogue of DT theory, the study of sheaves on Calabi-Yau 3-folds.
The generating series of BPS invariants for interesting quivers with potentials are in general very wild. However, using the Kontsevich-Soibelman wall-crossing formula, a recursive formula expresses the BPS invariants in terms of so-called attractor invariants, which are expected to be simple in interesting situations. We will discuss them for quivers with potential associated to triangulations of surfaces and quivers with potential giving noncommutative resolutions of CY3 singularities.
Tue, 11 Mar 2025
16:00
L6

On non-Gaussian multiplicative chaos

Mo Dick Wong
(Durham University)
Abstract

We consider two approximation schemes for the construction of a class of non-Gaussian multiplicative chaos, and show that they give rise to the same limit in the entire subcritical regime. Our approach uses a modified second moment method with the help of a new coupling argument, and does not rely on any Gaussian approximation or thick point analysis. As an application, we extend the martingale central limit theorem for partial sums of random multiplicative functions to L^1 twists. This is a joint work with Ofir Gorodetsky.

Tue, 04 Mar 2025
16:00
L6

Fermionic structure in the Abelian sandpile and the uniform spanning tree

Alessandra Cipriani
(University College London)
Abstract
In this talk we consider a stochastic system of sand grains moving on a finite graph: the Abelian sandpile, a prototype of self-organized lattice model. We focus on the function that indicates whether a single grain of sand is present at a site, and explore its connections with the discrete Gaussian free field, the uniform spanning tree, and the fermionic Gaussian free field. Based on joint works with L. Chiarini (Durham), R. S. Hazra (Leiden), A. Rapoport and W. Ruszel (Utrecht).



 

Tue, 25 Feb 2025
16:00
L6

The Critical 2d Stochastic Heat Flow and some first properties

Nikos Zygouras
(University of Warwick)
Abstract

The Critical 2d Stochastic Heat Flow arises as a non-trivial solution
of the Stochastic Heat Equation (SHE) at the critical dimension 2 and at a phase transition point.
It is a log-correlated field which is neither Gaussian nor a Gaussian Multiplicative Chaos.
We will review the phase transition of the 2d SHE, describe the main points of the construction of the Critical 2d SHF
and outline some of its features and related questions. Based on joint works with Francesco Caravenna and Rongfeng Sun.

Tue, 18 Feb 2025
16:00
L6

Fluctuations of the ground-state energy of the elastic manifold

Bertrand Lacroix-A-Chez-Toine
(Kings College London)
Abstract

In this talk I will consider properties of the disordered elastic manifold, describing an N-dimensional field u(x) defined for sites x of a d-dimensional lattice of linear size L. This prototypical model is used to describe interfaces in a wide range of physical systems [1]. I will consider properties of the ground-state energy for this model whose optimal configuration u_0(x) results from a compromise between the disorder which tend to favour sharp variations of the field and elastic interactions that smoothen them. I will study in particular the limit of large N>>1 and finite d which has been studied extensively in the physics literature (notably using the replica approach) [1,2] and has recently been considered in a series of paper by Ben Arous and Kivimae [3,4]. For this model, we compute exactly the large deviation function of the ground-state energy E_0, showing that it displays replica-symmetry breaking transitions. As an interesting outcome of this study, we show analytically the validity of the scaling law conjectured by Mezard and Parisi [2] for the variance of the ground-state energy. The latter relates the exponent of the variance Var(E_0)\sim L^{2\theta} such that \theta=2\zeta+d-2 with \zeta the exponent characterising the transverse fluctuations of the optimal configuration u_0(x), i.e.  (u_0(x)-u_0(x+y))^2\sim |y|^{2\zeta}. This work is done in collaboration with Y.V. Fyodorov (KCL) and P. Le Doussal (LPENS, CNRS).

 

[1] Giamarchi, T., & Le Doussal, P. (1998). Statics and dynamics of disordered elastic systems. In Spin glasses and random fields (pp. 321-356).

 

[2] Mézard, M., & Parisi, G. (1991). Replica field theory for random manifolds. Journal de Physique I1(6), 809-836.

 

[3] Ben Arous, G., & Kivimae, P. (2024). The Free Energy of the Elastic Manifold. arXiv preprint arXiv:2410.19094.

 

[4] Ben Arous, G., & Kivimae, P. (2024). The larkin mass and replica symmetry breaking in the elastic manifold. arXiv preprint arXiv:2410.22601.

Tue, 28 Jan 2025
16:00
L6

Zigzag strategy for random matrices

Sven Joscha Henheik
(IST Austria)
Abstract

It is a remarkable property of random matrices, that their resolvents tend to concentrate around a deterministic matrix as the dimension of the matrix tends to infinity, even for a small imaginary part of the involved spectral parameter.
These estimates are called local laws and they are the cornerstone in most of the recent results in random matrix theory. 
In this talk, I will present a novel method of proving single-resolvent and multi-resolvent local laws for random matrices, the Zigzag strategy, which is a recursive tandem of the characteristic flow method and a Green function comparison argument. Novel results, which we obtained via the Zigzag strategy, include the optimal Eigenstate Thermalization Hypothesis (ETH) for Wigner matrices, uniformly in the spectrum, and universality of eigenvalue statistics at cusp singularities for correlated random matrices. 
 

Based on joint works with G. Cipolloni, L. Erdös, O. Kolupaiev, and V. Riabov.

Tue, 21 Jan 2025
16:00
L6

Typical hyperbolic surfaces have an optimal spectral gap

Laura Monk
(University of Bristol )
Abstract
The first non-zero Laplace eigenvalue of a hyperbolic surface, or its spectral gap, measures how well-connected the surface is: surfaces with a large spectral gap are hard to cut in pieces, have a small diameter and fast mixing times. For large hyperbolic surfaces (of large area or large genus g, equivalently), we know that the spectral gap is asymptotically bounded above by 1/4. The aim of this talk is to present an upcoming article, joint with Nalini Anantharaman, where we prove that most hyperbolic surfaces have a near-optimal spectral gap. That is to say, we prove that, for any ε>0, the Weil-Petersson probability for a hyperbolic surface of genus g to have a spectral gap greater than 1/4-ε goes to one as g goes to infinity. This statement is analogous to Alon’s 1986 conjecture for regular graphs, proven by Friedman in 2003. I will present our approach, which shares many similarities with Friedman’s work, and relies on creating cancellations in the trace method.
 
The focus of this talk will be mostly analytic as I will present its geometric components at the GGT seminar. Both talks will be disjoint and independent, with the intention that they can be viewed either separately or together.
Nonlinear partial differential equations in neuroscience: from modelling to mathematical theory
Carrillo De La Plata, J Roux, P Mathematical Models and Methods in Applied Sciences volume 35 issue 2 403-584 (04 Mar 2025)
Thu, 13 Mar 2025

12:00 - 12:30
Lecture room 5

FUSE: the finite element as data

India Marsden
(Mathematical Institute (University of Oxford))
Abstract

The Ciarlet definition of a finite element has been core to our understanding of the finite element method since its inception. It has proved particularly useful in structuring the implementation of finite element software. However, the definition does not encapsulate all the details required to uniquely implement an element, meaning each user of the definition (whether a researcher or software package) must make further mathematical assumptions to produce a working system. 

The talk presents a new definition built on Ciarlet’s that addresses these concerns. The novel definition forms the core of a new piece of software in development, FUSE, which allows the users to consider the choice of finite element as part of the data they are working with. This is a new implementation strategy among finite element software packages, and we will discuss some potential benefits of the development.

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