Mészáros's critical-distribution conjecture for band-matrix cokernels

From papers

Let pp be prime. For each tR+t\in\mathbb{R}_+, let νt\nu_t be a distribution on the set of finite abelian pp-groups. Let n1<n2<n_1<n_2<\dots be positive integers, and let BiB_i be a Haar-uniform ni×nin_i\times n_i band matrix over Zp\mathbb{Z}_p with band width wiw_i. Assume that

limipwini=t.\lim_{i\to\infty}p^{-w_i}n_i=t.

Mészáros's critical-distribution conjecture. For every finite abelian pp-group GG,

limiP(cok(Bi)G)=νt(G).\lim_{i\to\infty}\mathbb{P}\bigl(\operatorname{cok}(B_i)\cong G\bigr)=\nu_t(G).

This conjecture predicts a one-parameter family of limiting cokernel distributions at the critical scale separating Cohen–Lenstra and non-Cohen–Lenstra behavior. The source states that the conjecture is still open.

Progress summary

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Sources & referencesView supporting material

Primary source

András Mészáros, “The rank evolution of block bidiagonal matrices over finite fields”, arXiv:2504.12275 (2025).

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