\'Etale homological stability and arithmetic statistics

TL;DR

This paper links homological stability in topology to arithmetic statistics over finite fields, providing new examples of étale cohomology stability and applying these results to compute asymptotic point counts.

Contribution

It introduces the first examples of étale cohomology stability as Galois representations and connects topological stability methods to arithmetic statistics.

Findings

Established étale homological stability for configuration spaces

Derived subexponential bounds on unstable cohomology growth

Computed large n limits of arithmetic statistics for varieties over finite fields

Abstract

We contribute to the arithmetic/topology dictionary by relating asymptotic point counts and arithmetic statistics over finite fields to homological stability and representation stability over $\Cb$ in the example of configuration spaces of $n$ points in smooth varieties. To do this, we import the method of homological stability from the realm of topology into the theory of \'{e}tale cohomology; in particular we give the first examples of stability of \'{e}tale cohomology groups as Galois representations where the Galois actions are not already explicitly known. We then establish subexponential bounds on the growth of the unstable cohomology, and we apply this and \'etale homological stability to compute the large $n$ limits of various arithmetic statistics of configuration spaces of varieties over $\F_q$.