English

Primes of bad reduction for systems of polynomial equations

Commutative Algebra 2026-03-04 v1 Algebraic Geometry

Abstract

Consider polynomials F1,,FsF_1,\dots,F_s in \K[X1,,Xn]\K[X_1,\dots,X_n] over a field \K\K, their zero-set V(F1,,Fn)V(F_1,\dots,F_n) in \Kbarn\Kbar^n and its decomposition into equidimensional components V0,,VnV_0,\dots,V_n (with ViV_i either empty or of dimension ii for all ii). To each ViV_i, we can associate its Chow forms, which are polynomials in new variables (Uk,j)0ki,0jn(U_{k,j})_{0\le k\le i, 0 \le j \le n}, uniquely defined up to a scalar factor. These Chow forms completely characterize ViV_i: we can recover equations for ViV_i from them, and their degree is (i+1)(i+1) times the degree of ViV_i. We discuss the situation when the FiF_i's have integer coefficients, and study the question of when the Chow forms of the ViV_i's defined as above can be reduced modulo pp to give Chow forms of the equidimensional components of V(F1modp,,Fsmodp)V(F_1 \bmod p,\dots,F_s \bmod p). We show that this is the case as soon as pp does not divide a certain nonzero integer Δ\Delta of height O(n14shd3n+4)O(n^{14} s h d^{3n+4}), with dd and hh bounds on respectively the degrees and heights of the FiF_i's.

Keywords

Cite

@article{arxiv.2603.02279,
  title  = {Primes of bad reduction for systems of polynomial equations},
  author = {Jesse Elliott and Éric Schost},
  journal= {arXiv preprint arXiv:2603.02279},
  year   = {2026}
}

Comments

Submitted to Journal of Symbolic Computation