English

Twisted Diophantine approximation for matrix transformations of tori

Number Theory 2025-11-20 v1

Abstract

Consider a sequence of integral matrices A=(An)nN\mathcal{A}=(A_n)_{n\in\N}, and a dd-tuple function r=(r1,,rd) ⁣:N(0,12){\bf r}=(r_1,\ldots,r_d)\colon \N\to (0,\frac{1}{2}). For a fixed vector α,{\bm \alpha}, we are interested in the set Tα(A,r)\mathcal{T}_{{\bm \alpha}}(\mathcal{A}, {\bf r}) of vectors β[0,1)d{\bm \beta}\in[0,1)^{d} for which Anα   ⁣ ⁣ ⁣ ⁣ ⁣(mod1)A_n{\bm \alpha}~~\!\!\!\!\!\pmod{1} infinitely often lies in the box centred at β{\bm \beta}, with side lengths 2ri(n)2r_i(n) in each coordinate direction. Under mild conditions on A\mathcal{A} and r{\bf r}, we prove a metric dichotomy for the size of Tα(A,r),\mathcal{T}_{{\bm \alpha}}(\mathcal{A}, {\bf r}), valid for almost every α{\bm \alpha} with respect to any fractal measure with a certain polynomial Fourier decay rate. Furthermore, removing all restrictions on r{\bf r}, we establish a metric dichotomy for Lebesgue almost every α.{\bm \alpha}. This solves a variant of a conjecture of Gonz\'{a}lez Robert, Hussain, Shulga and Ward [Conjecture 1.10, Bull. London Math. Soc. 2025]. Finally, we also establish a Jarn\'{i}k-type theorem for Tα(A,r).\mathcal{T}_{{\bm \alpha}}(\mathcal{A}, {\bf r}).

Keywords

Cite

@article{arxiv.2511.14954,
  title  = {Twisted Diophantine approximation for matrix transformations of tori},
  author = {Sam Chow and Qing-Long Zhou},
  journal= {arXiv preprint arXiv:2511.14954},
  year   = {2025}
}
R2 v1 2026-07-01T07:44:22.323Z