English

On an effective variation of Kronecker's approximation theorem avoiding algebraic sets

Number Theory 2018-02-01 v1

Abstract

Let ΛRn\Lambda \subset \mathbb R^n be an algebraic lattice, coming from a projective module over the ring of integers of a number field KK. Let ZRn\mathcal Z \subset \mathbb R^n be the zero locus of a finite collection of polynomials such that ΛZ\Lambda \nsubseteq \mathcal Z or a finite union of proper full-rank sublattices of Λ\Lambda. Let K1K_1 be the number field generated over KK by coordinates of vectors in Λ\Lambda, and let L1,,LtL_1,\dots,L_t be linear forms in nn variables with algebraic coefficients satisfying an appropriate linear independence condition over K1K_1. For each ε>0\varepsilon > 0 and aRn\boldsymbol a \in \mathbb R^n, we prove the existence of a vector xΛZ\boldsymbol x \in \Lambda \setminus \mathcal Z of explicitly bounded sup-norm such that Li(x)ai<ε\| L_i(\boldsymbol x) - a_i \| < \varepsilon for each 1it1 \leq i \leq t, where  \|\ \| stands for the distance to the nearest integer. The bound on sup-norm of x\boldsymbol x depends on ε\varepsilon, as well as on Λ\Lambda, KK, Z\mathcal Z and heights of linear forms. This presents a generalization of Kronecker's approximation theorem, establishing an effective result on density of the image of ΛZ\Lambda \setminus \mathcal Z under the linear forms L1,,LtL_1,\dots,L_t in the tt-torus~Rt/Zt\mathbb R^t/\mathbb Z^t.

Keywords

Cite

@article{arxiv.1801.10179,
  title  = {On an effective variation of Kronecker's approximation theorem avoiding algebraic sets},
  author = {Lenny Fukshansky and Nikolay Moshchevitin},
  journal= {arXiv preprint arXiv:1801.10179},
  year   = {2018}
}

Comments

13 pages, to appear in the Proceedings of AMS

R2 v1 2026-06-23T00:04:44.060Z