English

Finiteness of the Tate-Shafarevich group over function fields for groups of multiplicative type

Number Theory 2026-07-16 v1 Algebraic Geometry

Abstract

Let K=k(X)K = k(X) be the function field of a smooth geometrically integral variety XX of dimension 2\geq 2 over a field kk of characteristic 0 and VV be the set of discrete valuations of KK associated with the prime divisors on XX. We show that if DD is a kk-defined group of multiplicative type, then the corresponding Tate-Shafarevich group Sha(D,V)=ker(H1(K,D)vVH1(Kv,D))Sha(D,V) = \ker \left(H^1(K,D) \to \prod_{v \in V} H^1(K_v, D) \right) is finite in the following situations: (1) kk is finitely generated and X(k)X(k) \neq \emptyset; (2) kk is a number field. This complements previous work of Harari and Szamuely, which considered the case where XX is a curve.

Keywords

Cite

@article{arxiv.2607.15372,
  title  = {Finiteness of the Tate-Shafarevich group over function fields for groups of multiplicative type},
  author = {Igor A. Rapinchuk and Avinash Roy},
  journal= {arXiv preprint arXiv:2607.15372},
  year   = {2026}
}