Cheong and Kaplan's polynomial push-forward cokernel conjecture

Let P(t)Zp[t]P(t) \in \mathbb{Z}_p[t] be a non-constant monic square-free polynomial, written as

P(t)=P1(t)Pl(t),P(t)=P_1(t)\cdots P_l(t),

where each Pj(t)Zp[t]P_j(t)\in\mathbb{Z}_p[t] is monic and its reduction Pˉj(t)\bar{P}_j(t) modulo pp is distinct and irreducible in Fp[t]\mathbb{F}_p[t]. For a finite Zp[t]/(P(t))\mathbb{Z}_p[t]/(P(t))-module GG, let AnMn(Fp)A_n\in\mathrm{M}_n(\mathbb{F}_p) satisfy cok(Pˉ(An))Fp[t]G/pG\operatorname{cok}(\bar{P}(A_n))\simeq_{\mathbb{F}_p[t]}G/pG. Write qj=pdeg(Pj)q_j=p^{\deg(P_j)}, let Fqj=Fp[t]/(Pˉj(t))\mathbb{F}_{q_j}=\mathbb{F}_p[t]/(\bar{P}_j(t)), and set rqj(G)=dimFqj(G/pGFp[t]Fqj)r_{q_j}(G)=\dim_{\mathbb{F}_{q_j}}(G/pG\otimes_{\mathbb{F}_p[t]}\mathbb{F}_{q_j}). Cheong and Kaplan's conjecture. One must have

ProbXMn(Zp)Haar(cok(P(X))Zp[t]GXAn(modp))=1AutZp[t](G)j=1lprqj(G)2i=1rqj(G)(1qji)2.\operatorname{Prob}_{X\in\mathrm{M}_n(\mathbb{Z}_p)^{\mathrm{Haar}}}\left(\operatorname{cok}(P(X))\simeq_{\mathbb{Z}_p[t]}G\mid X\equiv A_n\pmod p\right)=\frac{1}{|\operatorname{Aut}_{\mathbb{Z}_p[t]}(G)|}\prod_{j=1}^{l}p^{r_{q_j}(G)^2}\prod_{i=1}^{r_{q_j}(G)}(1-q_j^{-i})^2.

This conjecture generalizes results of Friedman and Washington and subsequent special cases proved by the authors, Cheong and Kaplan, and Cheong, Liang, and Strand; it predicts the conditional distribution of cokernels of polynomial images of random integral matrices when the polynomial has distinct irreducible residue factors.

Sources & referencesView supporting material

Primary source

Gilyoung Cheong and Yifeng Huang, “The cokernel of a polynomial push-forward of a random integral matrix with concentrated residue”, arXiv:2310.09491 (2023).

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