# Probability seminars 2017/2018

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Title: Jacobi triple product via the exclusion process

Speaker: Marton Balazs (Bristol)

Date: Wednesday, 17th January 2018

Time: 2pm

Location: UCD, S3.56 Science South

Abstract: I will give a brief overview of very simple, hence maybe less investigated structures in interacting particle systems: reversible product blocking measures. These turn out to be more general than most people would think, in particular asymmetric simple exclusion and nearest-neighbour asymmetric zero range processes both enjoy them. But a careful look reveals that these two are really the same process. Exploitation of this fact will give rise to the Jacobi triple product formula - an identity previously known from number theory and combinatorics. I will derive it from pure probability this time, and I hope to surprise my audience as much as we got surprised when this identity first popped up in our notebooks.

Date: Wednesday, 24th January 2018

Time: 2pm

Location: UCD, 125 Science North (JK Lab)

Speaker: Theodoros Assiotis (Warwick)

Title: "Determinantal structures in (2+1)-dimensional growth and decay models."

**Abstract:** "I will talk about an inhomogeneous growth and decay model with a wall present in which the growth and decay rates on a single horizontal slice of the surface can be chosen essentially arbitrarily depending on the position. This model turns out to have a determinantal structure and most remarkably for a certain, the fully packed, initial condition the correlation kernel can be calculated explicitly in terms of one dimensional orthogonal polynomials on the positive half line and their orthogonality measures."

**Title: ** "The genealogical structure of Galton-Watson trees."

**Speaker:** Samuel Johnston (UCD)

**Date: ** Wednesday, 31st January 2018

**Time:** 2pm

**Location:** Room 1.25 O’Brien Centre for Science North**Abstract:**

Consider a continuous-time Galton-Watson branching process. If we condition the population to survive until a large fixed time T, and then choose k individuals at random from those alive at that time, what does the ancestral tree relating these k individuals look like?

**Title:** Tableaux combinatorics and the Abelian sandpile model on two classes of graphs**Speaker:** Mark Dukes (UCD)**Date:** Wednesday, 7th February 2018**Time:** 2pm**Location:** UCD, 125 Science North (JK Lab)**Abstract:**

The Abelian sandpile model is a model of discrete diffusion and can be considered as a process on any abstract graph. A state of the model is an assignment of grains of sand to vertices of the graph. If the number of grains at a vertex is less than its degree then that vertex is called stable, and a stable state is one in which every vertex is stable. However, should the number of grains at a vertex exceed its degree, then this vertex may topple and send a grain of sand to each of its neighbours. Recurrent states of this model are those stable states that appear in the long term limit. In this talk I will outline a collection of results concerning recurrent states of the sandpile model on both the complete bipartite graph and the Ferrers graph.

**Title:** Two-time distribution in last-passage percolation**Speaker:** Kurt Johansson (Stockholm)**Date:** Wednesday, 14th February 2018**Time:** 2pm**Location:** UCD, 125 Science North (JK Lab)**Abstract:**

I will discuss a new approach to computing the two-time distribution in last-passage

percolation with geometric weights. This can be interpreted as the correlations of the height

function at a spatial point at two different times in the equivalent interpretation as a discrete

polynuclear growth model. The new approach is rather close to standard random matrix theory

(or determinantal point process) computations. I will give some background and also present

some aspects of the computations involved.

**Speaker:** Philippe Biane (Paris)

**Title:** Gog and Magog triangles and the Schutzenberger involution

**Date:** Wednesday, 7th March 2018

**Time:** 2pm

**Location:** UCD, 125 Science North (JK Lab)

**Abstract:** I will present Gog and Magog triangles which are particular cases of Gelfand-Tsetlin triangles and which appear in many models of statistical mechanics. An open problem is to find a bijection between these classes of objects. I will explain an approach to this problem based on the Schutzenberger involution.

All are welcome.

**Title:** The two dimensional Yang-Mills measure and its large N limit**Speaker: ** Antoine Dahlqvist (UCD)**Date:** Wednesday, 14th Mar 2018**Time:** 2pm**Location:** UCD, 125 Science North (JK Lab)**Abstract:**

The Yang-Mills measure is a model of mathematical physics that stems from the physics of the standard model, describing the interactions between elementary particles. We shall explain how it gives raise to random matrix models in two dimensions that are very closely related to the Brownian motion on compact Lie groups. Given a surface, playing the role of space-time, and a compact Lie group, associated to the type of interaction, it is the data of a random mapping that sends any path to a matrix of the group in a multiplicative way. From the pioneering work of G. t’Hooft, it was conjectured in the physics literature that these models simplify when, the surface being kept fixed, the dimension of the group goes to infinity. We shall see that they display different behaviors in regards of the choice of surface and how they can be analysed thanks to differential equations involving deformations of loops, known as Makeenko-Migdal equations.

**Title:** Large deviations for non-interacting trapped fermions

**Speaker:** Gregory Schehr (Orsay)

**Date:** Wednesday, 21st March 2018

**Time:** 2pm

**Location:** UCD, 125 Science North (JK Lab)

**Abstract:** I will consider the (quantum) spatial fluctuations of N non-interacting fermions in an isotropic d-dimensional trapping potential at zero temperature, with a special focus on hard potentials. I will study the maximal radial distance, $r_{\max}$, of the fermions from the trap center and focus on the large deviations of $r_{\max}$ away from its typical position, both to the right (right tail) and to the left (left tail). In $d=1$, this question can be studied, in several cases, thanks to an exact mapping to random matrix models, where such large deviations regimes have been well studied in the recent past. I will show that in $d>1$ the large deviation regime to the left exhibits a quite unusual, and rather universal, intermediate regime. This intermediate regime can be studied in detail using the tools of determinantal point processes.

**Speakers:** Pierre Le Doussal and Alexandre Krajenbrink (Paris)

**Title:** Large deviation tails for the KPZ equation

**Date:** Wednesday, 18th April 2018

**Time:** 1.30pm - 3pm *** Note slightly earlier than usual time ***

**Location:** UCD, 125 Science North (JK Lab)

**Abstract:** We present informally recent results on the large deviations for the distribution of the height of a growing interface described by the Kardar-Parisi-Zhang equation. The large time large deviation rate function is calculated using Coulomb gas methods. The short time rate functions are also obtained for several initial conditions. The numerical determination of the rate function is in good agreement with the predictions.

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