English

Reductions of points on algebraic groups, II

Number Theory 2021-07-01 v1

Abstract

Let AA be the product of an abelian variety and a torus over a number field KK, and let mm be a positive integer. If αA(K)\alpha \in A(K) is a point of infinite order, we consider the set of primes p\mathfrak p of KK such that the reduction (αmodp)(\alpha \bmod \mathfrak p) is well defined and has order coprime to mm. This set admits a natural density, which we are able to express as a finite sum of products of \ell-adic integrals, where \ell varies in the set of prime divisors of mm. We deduce that the density is a rational number, whose denominator is bounded (up to powers of mm) in a very strong sense. This extends the results of the paper "Reductions of points on algebraic groups" by Davide Lombardo and the second author, where the case mm prime is established.

Keywords

Cite

@article{arxiv.1802.08527,
  title  = {Reductions of points on algebraic groups, II},
  author = {Peter Bruin and Antonella Perucca},
  journal= {arXiv preprint arXiv:1802.08527},
  year   = {2021}
}
R2 v1 2026-06-23T00:31:23.394Z