On Some Properties of Irrational Subspaces

Abstract: In this paper we discuss some properties of completely irrational subspaces. We prove that there exist completely irrational subspaces that are badly approximable and, moreover, sets of such subspaces are winning in different senses. We get some bounds for Diophantine exponents of vectors that lie in badly approximable subspaces that are completely irrational; in particular, for any vector $\xi$ from two-dimensional badly approximable completely irrational subspace of $\mathbb{R}^d$ one has $\hat{\omega}(\xi) \leq \frac{\sqrt{5} - 1}{2}$. Besides that, some statements about the dimension of subspaces generated by best approximations to completely irrational subspace easily follow from properties that we discuss.