Hausdorff dimension of the set of singular pairs

In this paper we show that the Hausdorff dimension of the set of singular pairs is 4 3 . We also show that the action of diag(e t , e t , e -2t ) on SL3R/SL3Z admits divergent trajectories that exit to infinity at arbitrarily slow prescribed rates, answering a question of A. N. Starkov. As a by-product of the analysis, we obtain a higher-dimensional generalization of the basic inequalities satisfied by convergents of continued fractions. As an illustration of the technique used to compute Hausdorff dimension, we reprove a result of I. J. Good asserting that the Hausdorff dimension of the set of real numbers with divergent partial quotients is 1 2 .