Geometric and arithmetic aspects of approximation vectors

Abstract

Let $\theta\in\mathbb{R}^d$. We associate three objects to each approximation $(p,q)\in \mathbb{Z}^d\times \mathbb{N}$ of $\theta$: the projection of the lattice $\mathbb{Z}^{d+1}$ to the hyperplane of the first $d$ coordinates along the approximating vector $(p,q)$; the displacement vector $(p - q\theta)$; and the residue classes of the components of the $(d + 1)$-tuple $(p, q)$ modulo all primes. All of these have been studied in connection with Diophantine approximation problems. We consider the asymptotic distribution of all of these quantities, properly rescaled, as $(p, q)$ ranges over the best approximants and $\epsilon$-approximants of $\theta$, and describe limiting measures on the relevant spaces, which hold for Lebesgue a.e. $\theta$. We also consider a similar problem for vectors $\theta$ whose components, together with 1, span a totally real number field of degree $d+1$. Our technique involve recasting the problem as an equidistribution problem for a cross-section of a one-parameter flow on an adelic space, which is a fibration over the space of $(d + 1)$-dimensional lattices. Our results generalize results of many previous authors, to higher dimensions and to joint equidistribution.