Equidistribution of non-uniformly stretching translates of shrinking smooth curves and weighted Dirichlet approximation

Abstract

We show that under the action of $\mathrm{diag}(e^{nt},e^{-r_1(t)},\ldots,e^{-r_n(t)})\in\mathrm{SL}(n+1,\mathbb{R})$, where $r_i(t)\to\infty$, on the space of unimodular lattices in $\mathbb{R}^{n+1}$, the translates of any fixed-sized piece of a `non-degenerate' smooth curve, or a shrinking piece of size $e^{-t}$ about almost any point of the curve, get equidistributed in the space as $t\to\infty$. From this, it follows that the weighted Dirichlet approximation theorem cannot be improved for almost all points on any non-degenerate $C^{2n}$ curve in $\mathbb{R}^n$. This result extends the corresponding result for analytic curves due to Shah (2009) and answers some questions inspired by the work of Davenport and Schmidt (1969) and Kleinbock and Weiss (2008).