Eigenvalue Distribution of $p$-adic Random Matrices Among Algebraic Extensions, with an Analogue for $p$-adic Random Polynomials

TL;DR

This paper investigates the eigenvalue distribution of Haar-random matrices over $ ext{Z}_p$ in algebraic extensions, providing $p$-adic analogues of real eigenvalue counting results and analyzing their distribution among extension degrees.

Contribution

It introduces $p$-adic analogues of real eigenvalue counting results, analyzing eigenvalue distribution among algebraic extensions and their relation to unramified extensions.

Findings

$p$-adic eigenvalues are evenly distributed among extension degrees asymptotically.

Maximal unramified extension captures all but a bounded expected number of eigenvalues.

Results extend to roots of random Haar polynomials over $ ext{Z}_p$ with similar behavior.

Abstract

We study the distribution of eigenvalues of Haar-random matrices over $\mathbb{Z}_p$ among algebraic extensions of $\mathbb{Q}_p$. Our results give $p$-adic analogues of the real-eigenvalue counting results of Edelman-Kostlan-Shub for the real Ginibre ensemble, but with a different degree behavior: while real eigenvalues form only a vanishing proportion in the real Ginibre ensemble, $p$-adic eigenvalues are asymptotically evenly distributed among possible extension degrees. We also show that the maximal unramified extension $\mathbb{Q}_p^{\mathrm{un}}$ captures all but a bounded expected number of eigenvalues, and that the expected number of eigenvalues outside $\mathbb{Q}_p^{\mathrm{un}}$ has a finite positive limit with an explicit upper bound. The proof uses correlation function formulas from the author's previous joint work with Van Peski (arXiv:2601.06283), together with uniform estimates over varying finite extensions. We also prove analogous results for roots of random Haar polynomials over $\mathbb{Z}_p$, using the correlation function formulas of Caruso (arXiv:2110.03942). These polynomial results are $p$-adic analogues of the real-root counting results of Edelman-Kostlan, again with behavior different from the real setting.