# Universal singularity at the closure of a gap in a random matrix theory

Research paper by E. Brezin, S. Hikami

Indexed on: 03 Apr '98Published on: 03 Apr '98Published in: Physics - Statistical Mechanics

#### Abstract

We consider a Hamiltonian $H = H_0+ V$, in which $H_0$ is a given non-random Hermitian matrix,and $V$ is an $N \times N$ Hermitian random matrix with a Gaussian probability distribution.We had shown before that Dyson's universality of the short-range correlations between energy levels holds at generic points of the spectrum independently of $H_{0}$. We consider here the case in which the spectrum of $H_{0}$ is such that there is a gap in the average density of eigenvalues of $H$ which is thus split into two pieces. When the spectrum of $H_{0}$ is tuned so that the gap closes, a new class of universality appears for the energy correlations in the vicinity of this singular point.