Stationary hitting times on vertex-transitive graphs

TL;DR

This paper refines bounds on stationary hitting times for reversible Markov chains, especially on vertex-transitive graphs, with implications for understanding cover time fluctuations.

Contribution

It provides improved bounds on stationary hitting times for vertex-transitive graphs, refining previous exponential approximation results.

Findings

Enhanced bounds for hitting times in low-dimensional tori

Error terms are quadratically smaller in dimensions less than four

Results are crucial for characterizing cover time fluctuations

Abstract

We prove a refined version of the Aldous and Brown's exponential approximation of stationary hitting times. These are valid for all reversible Markov chains. We then specialise our estimates for vertex-transitive graphs, where we obtain improved bounds which depend on the growth of the graphs. The most delicate cases are when the diameter is comparable to that of low-dimensional tori. In particular, in "dimensions" less than four (up to logarithmic factors) our error terms are the square of those of Aldous and Brown. These improved bounds play a crucial role in the companion work arXiv:2202.02255 characterising the fluctuations of the cover time on vertex-transitive graphs.