Date 
Speaker 
Title 
8/30/17 
Thomasz Luks
Universität Paderborn 
Multiple points of operator stable Lévy processes
Abstract
The existence and Hausdorff dimension of multiple points of paths have been intensely studied for Brownian motion and more general Lévy processes. The purpose of this talk is to present some new results in this area for a class of Lévy processes called operator stable Lévy processes. Under additional symmetry assumption, we will give an explicit dimension formula for the set of multiple points in terms of the eigenvalues of the stability exponent, which is a nonsingular square matrix. We will also discuss an existence criterion for multiple points. The talk is based on a joint project with Yimin Xiao.

9/6/17 
Yanghui Liu
Purdue University 
Weighted limit theorems and applications
Abstract
The term limit theorem is associated with a multitude of statements having to do with the convergence of probability distributions of sums of increasing number of random variables. Given that a limit theorem result holds, weighted limit theorem in this talk is referred to the problem: what is the asymptotic behavior of the corresponding weighted sums? The problem has drawn a lot of attention in recent articles due to its essential role in topics such as timediscrete numerical schemes, parameter estimations, Ito’s formula in law, and normal approximations, and various unexpected weighted limit theorems have been discovered since then. The purpose of this talk is to introduce a universal and surprisingly simple framework for this problem, and to provide generalizations of the existing results in a few aspects.

9/13/17 
Rodrigo Bañuelos
Purdue University 
Stability in martingales inequalities and singular integrals
Abstract
The study of the stability of various classical inequalities in analysis and geometry (Sobolev, HardyLittlewoodSobolev, Nash, HousdorffYoung, isoperimetric, FaberKrahn, etc.) has received a lot of attention in recent years. Following the seminal work of Burkholder in the 80's, there has been considerable interest in sharp inequalities for martingales and their applications to various problems in analysis. Unlike many sharp inequalities in analysis and geometry, extremals for these inequalities do not exist and equality is never attained except for trivial cases. In this talk we discuss the nature and stability of the almost extremals in Burkholder's inequalities for differentially subordinate martingales and extensions to orthogonal martingales that arise in several problems. As an application we present similar results for the real and imaginary parts of the BerulingAhlfors operator and other singular integrals. This talk is based on join work with Adam Oscekowski of the University of Warsaw.

9/20/17 
Daesung Kim
Purdue University 
Stability results for Logarithmic Sobolev inequality
Abstract
The logarithmic Sobolev inequality has been extensively studied in analysis and probability. After the equality case is fully characterized by E. Carlen, it is natural to ask how far an admissible function that is close to achieving the equality deviates from the optimizers. This question is called a stability for log Sobolev inequality. In this talk, we discuss stability results for Logarithmic Sobolev inequality in terms of the Wasserstein distance and the total variation distance. This is based on a joint work with Emanuel Indrei.

9/27/17 
Maylis Varvenne
Université de Toulouse 
Rate of convergence to equilibrium for discretetime stochastic dynamics with memory
Abstract
We are interested in a general class of recursive discrete dynamics : ${\scriptsize X_{n+1}=F(X_n,\Delta_{n+1})}$ where ${\scriptsize (\Delta_n)_{n\in \mathbb{Z}}}$ is an ergodic stationary Gaussian sequence. We can think for instance of fractional Brownian motion increments. First, we will see how it is possible to define invariant distributions in this a priori nonMarkovian setting. Then, after proving existence of such a distribution, we will get a uniqueness result and a rate of convergence to this invariant distribution in total variation distance. The proof is based on a coupling method (with a step which is specific to this nonMarkovian framework) first implemented by M.Hairer in a continuous time setting. This method was also used by J. Fontbona and F. Panloup, as well as A. Deya, F. Panloup and S. Tindel in order to extend M. Hairer's results.

10/4/17 
Ibrahim Ekren
University of Michigan 
Hörmander condition for delayed diffusions
Abstract
In this talk we present some results that extends the Hormander condition to delayed diffusions. We will state a sufficient condition for the existence of density for the marginals of a delayed diffusion. This condition takes into account and quantifies the additional noise introduced to the system through the delay. The talk is based on joint work with Reda Chhaibi.

10/11/17 
David Sivakoff
Ohio State University 
Parking on trees and lattices
Abstract
At each vertex of a graph ${\scriptsize G}$, independently place a car with probability ${\scriptsize p}$ and place a parking spot otherwise. Each car performs an independent random walk until it finds a vacant parking spot, at which time it parks in the spot. Each parking spot can be occupied by at most one car, with ties broken uniformly, and cars drive over occupied parking spots. Given ${\scriptsize G}$ and ${\scriptsize p}$, does every car eventually park? Do there exist parking spots that remain vacant forever? A phase transition in this model was recently observed by Lackner and Panholzer for uniform random directed trees on ${\scriptsize n}$ vertices, and by Goldschmidt and Przykucki on directed critical GaltonWatson trees. We prove that a phase transition occurs at ${\scriptsize p=1/2}$ when ${\scriptsize G}$ is any infinite, transitive, unimodular graph (including ${\scriptsize Z^d}$ and the ${\scriptsize (d+1)}$regular tree). This is joint work with Michael Damron, Janko Gravner, Matthew Junge and Hanbaek Lyu.

10/18/17 
Anirban DasGupta
Purdue University 
The randomly deleted factorial and lacunary series
Abstract
The talk addresses the following general question: consider random power series or random infinite products, and ask what are their limiting distributions, with centering and norming, or the exact distribution, when they converge almost surely. Of particular importance
in this seminar will be deleted series, or deleted products.
For example, take the series for ${\scriptsize e^x}$, and sum over a subsequence of
the natural numbers; or, take ${\scriptsize n!}$, and take the product over a
random subset of ${\scriptsize\{1, 2, \ldots, n\}}$.
The deleted series and the products are sometimes asymptotically Gaussian,
and sometimes something else. The centering sequence depends on how sparse
is the subsequence over which the deleted summation is performed.
A famous case will be revisited: the ErdösKahane problem of the distribution of INFINITE BERNOULLI CONVOLUTIONS. The question that
has attracted the most attention is when are infinite Bernoulli convolutions absolutely continuous. We know when they are not (those that
arise from reciprocals of PV numbers; Erdös already knew it); we know a few explicit cases when they are, due to A. Garsia. The deepest
but nonconcrete (to a practical person) are the results on
almost sure absolute continuity of such convolutions, and
(Hausdorff) dimensions of the complementary set. The seminar
will pose a (seemingly) nice related (and unattacked?) problem.

10/25/17 
Tal Orenshtein
Humbolt Univ. and TU Berlin 
Critical wetting models in (1+1) dimensions
Abstract
In this talk we will discuss wetting models in (1+1) dimensions pinned to a shrinking strip. Except for the space geometry effect (the one dimensional lattice, in our case) these polymer models enjoy an interplay between two forces  local (pinning) and global (entropic repulsion)  and one expects a localizationdelocalization phase transition to hold. When the strip size is fixed and the pinning function is constant and homogeneous, phase transition results are known, and moreover, the standard case (zero strip size) is completely solved and exhibits a sharp phase transition. In particular, the system behavior is drastically different in the three phases, subcriticality, super criticality and criticality. We will focus on shrinking strips at criticality.
Joint work in progress with JeanDominique Deuschel.

11/8/17 
Abram Magner
UIUC 
Symmetry, temporal information, and succinct representation of random graph structures
Abstract
I will discuss mathematical aspects of my recent work on two related problems at the intersection
of random graphs and information theory: (i) node arrival order inference  for a dynamic random
graph model, determine the extent to which the order in which nodes arrived can be inferred
from the graph structure, and (ii) compression of structures  for a given graph model,
exhibit an efficiently computable and invertible mapping from unlabeled graphs to bit strings
with minimum possible expected code length.
Both problems are connected to the study of the symmetries
of the graph model, as well as another combinatorial quantity  the typical number of
feasible labeled representatives of a given structure. I will focus on the case of the
preferential attachment model, for which we are able to give a (nearly) complete
characterization of the behavior of the size of the automorphism group, as well as a provably
asymptotically optimal algorithm for (ii). I will also discuss progress on efficiently computable optimal estimators for certain natural formulations of (i).

11/14/17 
Sandra Cerrai
University of Maryland 
On the validity of a large deviation principle for some nonlinear SPDEs with rough noise. This is a Math colloquium, at 3:30 in Math 175
Abstract
We are dealing with the study of the validity of a large deviation principle for some nonlinear PDEs, perturbed by a Gaussian random forcing. We are here interested in the regime where both the strength of the noise and its correlation are vanishing, on a length scale ${\scriptsize\epsilon}$ and ${\scriptsize\delta}$, respectively, with ${\scriptsize \epsilon}$ and ${\scriptsize\delta}$ small. Depending on the relationship between ${\scriptsize\epsilon}$ and ${\scriptsize\delta}$ we will prove the validity of the large deviation principle in different functional spaces. We will illustrate our method by considering the twodimensional stochastic NavierStokes equation and a class of stochastic reactiondiffusion equations, defined in any space dimension, including the dynamical ${\scriptsize\Phi^{2n}_d}$ model.

11/15/17 
Patrick Wolfe
Dean of Science and Statistics Department, Purdue University 
Nonparametric network comparison
Abstract
Understanding how two networks differ, or quantifying the degree to which a single network departs from a given model, is a challenging question in modern mathematical statistics. Here we show how subgraph densities, which for large graphs play a role analogous to moments in the context of random variables, enable a natural means of nonparametric network comparison. Coupled with a partial order derived from a notion of subgraph scale, we then show how this leads to an automated, computationally scalable comparison algorithm with provable properties. Joint work with P.A. Maugis and S. C. Olhede; preprint
here.

11/29/17 
Jon Peterson
Purdue University 
Quantitative CLTs for random walks in random environments
Abstract
The classical central limit theorem (CLT) states that for sums of a large number of i.i.d. random variables with finite variance, the distribution of the rescaled sum is approximately Gaussian. However, the statement of the central limit theorem doesn't give any quantitative error estimates for this approximation. Under slightly stronger moment assumptions, quantitative bounds for the CLT are given by the BerryEsseen estimates. In this talk we will consider similar questions for CLTs for random walks in random environments (RWRE). That is, for certain models of RWRE it is known that the position of the random walk has a Gaussian limiting distribution, and we obtain quantitative error estimates on the rate of convergence to the Gaussian distribution for such RWRE.
