# Difference between revisions of "Past Probability Seminars Spring 2020"

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− | Title: The fractal nature of the Abelian Sandpile | + | Title: '''The fractal nature of the Abelian Sandpile''' |

Abstract: The Abelian Sandpile is a simple diffusion process on the integer lattice, in which configurations of chips disperse according to a simple rule: when a vertex has at least 4 chips, it can distribute one chip to each neighbor. | Abstract: The Abelian Sandpile is a simple diffusion process on the integer lattice, in which configurations of chips disperse according to a simple rule: when a vertex has at least 4 chips, it can distribute one chip to each neighbor. |

## Revision as of 10:08, 8 February 2018

# Spring 2018

**Thursdays in 901 Van Vleck Hall at 2:25 PM**, unless otherwise noted.
**We usually end for questions at 3:15 PM.**

If you would like to sign up for the email list to receive seminar announcements then please send an email to join-probsem@lists.wisc.edu.

## Thursday, February 1, 2018, Hoi Nguyen, OSU

Title: **A remark on long-range repulsion in spectrum**

Abstract: In this talk we will address a "long-range" type repulsion among the singular values of random iid matrices, as well as among the eigenvalues of random Wigner matrices. We show evidence of repulsion under arbitrary perturbation even in matrices of discrete entry distributions. In many cases our method yields nearly optimal bounds.

## Thursday, February 8, 2018, Jon Peterson, Purdue

Title: **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 Berry-Esseen 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. This talk is based on joint works with Sungwon Ahn and Xiaoqin Guo.

## Friday, 4pm February 9, 2018, Van Vleck B239 Wes Pegden, CMU

** This is a probability-related colloquium---Please note the unusual room, day, and time! **

Title: **The fractal nature of the Abelian Sandpile**

Abstract: The Abelian Sandpile is a simple diffusion process on the integer lattice, in which configurations of chips disperse according to a simple rule: when a vertex has at least 4 chips, it can distribute one chip to each neighbor. Introduced in the statistical physics community in the 1980s, the Abelian sandpile exhibits striking fractal behavior which long resisted rigorous mathematical analysis (or even a plausible explanation). We now have a relatively robust mathematical understanding of this fractal nature of the sandpile, which involves surprising connections between integer superharmonic functions on the lattice, discrete tilings of the plane, and Apollonian circle packings. In this talk, we will survey our work in this area, and discuss avenues of current and future research.

## Thursday, February 15, 2018, TBA

## Thursday, February 22, 2018, Garvesh Raskutti UW-Madison Stats and WID

Title: TBA

## Thursday, March 8, 2018, TBA

## Thursday, March 15, 2018, Wenqing Hu Missouri S&T

TBa