Final doctoral examination and defense of dissertation of Emma Cohen

Monday, September 12, 2016 - 9:00am
Skiles 006
Title: Problems in Catalan mixing and matchings in regular hypergraphs
Advisor: Dr. Prasad Tetali, School of Mathematics
Committee: Dr. Santanu Dey, School of Industrial and Systems Engineering
  Dr. Milena Mihail, School of Computer Science
  Dr. Dana Randall, School of Computer Science
  Dr. William T. Trotter, School of Mathematics
Reader: Dr. David Galvin, Department of Mathematics, University of Notre Dame

This dissertation consists of two parts, falling under the closely related fields of counting and sampling.

In the first part, we explore the relationships between several natural notions of adjacency on Catalan structures and their associated random walks. We use a matroid interpretation of Dyck words of length 2n to give a new order n^2 bound on the mixing time for the transposition walk. We also give a general mixing bound for random walks on the Boolean cube when censored to remain within some large monotone subset.

In the second part, we extend several related extremal results about the number of matchings and independent sets in regular graphs. First we propose a method for tackling the Upper Matching Conjecture of Friedland, et al. for matchings of small fixed size. Next we prove a conjecture of Galvin regarding the extremal graph for number of Widom-Rowlinson configurations, a particular instance of graph homomorphisms. Finally, we make progress towards unifying the extremal bounds of Kahn, Galvin & Tetali, and Zhao for independent sets and of Davies, et al., for matchings by giving two general bounds for matchings in regular, uniform hypergraphs, improving on a similar bound due to Ordentlich & Roth.