The Distribution of the first Eigenvalue Spacing at the Hard Edge of the Laguerre Unitary Ensemble

Abstract

The distribution function for the first eigenvalue spacing in the Laguerre unitary ensemble of finite rank random matrices is found in terms of a Painlev\'e V system, and the solution of its associated linear isomonodromic system. In particular it is characterised by the polynomial solutions to the isomonodromic equations which are also orthogonal with respect to a deformation of the Laguerre weight. In the scaling to the hard edge regime we find an analogous situation where a certain Painlev\'e \IIId system and its associated linear isomonodromic system characterise the scaled distribution. We undertake extensive analytical studies of this system and use this knowledge to accurately compute the distribution and its moments for various values of the parameter $a$. In particular choosing $a=\pm 1/2$ allows the first eigenvalue spacing distribution for random real orthogonal matrices to be computed.Comment: 65 pages, 1 eps figure, typos and references correcte