2-Selmer groups of even hyperelliptic curves over function fields

Abstract

In this paper, we are going to compute the average size of 2-Selmer groups of families of even hyperelliptic curves over function fields. The result will be obtained by a geometric method which is based on a Vinberg’s representation of the group G = PSO ( 2 n + 2 ) G=\text {PSO}(2n+2) and a Hitchin fibration. Consistent with the result over Q \mathbb {Q} of Arul Shankar and Xiaoheng Wang [Compos. Math. 154 (2018), pp. 188–222], we provide an upper bound and a lower bound of the average. However, if we restrict to the family of transversal hyperelliptic curves, we obtain precisely average number 6.