Conjecture on derangement proportions in affine symplectic and orthogonal groups

From papers

Let qq be a prime power of odd characteristic, and let mm be a non-negative integer. For a finite group GG acting on a set, write 4δ(G)44\delta(G)4 for the proportion of derangements in GG. Let ASp2m(q)\operatorname{ASp}_{2m}(q), AO2m+1(q)\operatorname{AO}_{2m+1}(q) and AO2m±(q)\operatorname{AO}^{\pm}_{2m}(q) denote the affine symplectic and orthogonal groups in the indicated dimensions.

Derangement proportion conjecture. The following formulas hold:

δ(ASp2m(q))=1q+1(11(q)m(m+2)).\delta(\operatorname{ASp}_{2m}(q))=\frac{1}{q+1}\left(1-\frac{1}{(-q)^{m(m+2)}}\right). δ(AO2m+1(q))=12+(1)m12q(m+1)2.\delta(\operatorname{AO}_{2m+1}(q))=\frac{1}{2}+\frac{(-1)^{m-1}}{2q^{(m+1)^2}}. δ(AO2m±(q))=12±(1)m12qm(m+1).\delta(\operatorname{AO}^{\pm}_{2m}(q))=\frac{1}{2}\pm\frac{(-1)^{m-1}}{2q^{m(m+1)}}.

These formulas would give concise closed expressions for the derangement proportions in the affine symplectic and orthogonal cases. The paper reduces their proof to three qq-polynomial identities, which are stated separately as Conjecture identities; the supplied text does not establish those identities or resolve this conjecture.

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Sources & referencesView supporting material

Primary source

Jessica Anzanello, “On the proportion of derangements in affine classical groups”, arXiv:2508.07093 (2026).

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