Kac-Rice inspired approach to non-Hermitian random matrices

Yan V Fyodorov

Published 2025-06-26Version 1

We suggest a method of analyzing the joint probability density (JPD) ${\cal P}_N(z,{\bf v})$ of an eigenvalue $z$ and the associated right eigenvector ${\bf v}$ (normalized with ${\bf v}^*{\bf v}=1$) of non-Hermitian random matrices of a given size $N\times N$. The method, which represents an alternative to Girko Hermitization approach, is essentially based on the Kac-Rice counting formula applied to the associated characteristic polynomial combined with a certain integral identity for the Dirac delta function of such a polynomial. To illustrate utility of the general method we apply it to consider two particular cases: (i) one-parameter family of matrices interpolating between complex Ginibre and real Ginibre ensembles and (ii) a complex Ginibre matrix additively perturbed by a fixed matrix. In particular, in the former case we discuss the formation of an excess of eigenvalues in the vicinity of the real axis on approaching the real Ginibre limit, which eventually gives rise to the existence of a new scaling regime of "weak non-reality" as $N\to \infty$. In the second case we provide new insights into eigenvalue and eigenvector distribution for a general rank one perturbation of complex Ginibre matrices of finite size $N$, and in the structure of an outlier as $N\gg 1$. Finally we discuss a possible generalization of the proposed method which is expected to be suitable for analysis of JPD involving both left- and right eigenvectors.