Cohen–Lenstra–Soundararajan conjectural asymptotic for odd imaginary quadratic class numbers

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For an odd positive integer hh, let F(h)\mathcal{F}(h) be the number of negative fundamental discriminants dd with class number h(d)=hh(d)=h. Let Y(p)\mathbb{Y}(p) be independent random variables taking the values 11 and −1-1 with probability 1/21/2, and set

L(1,Y)=∏p(1−Y(p)p)−1.L(1,\mathbb{Y})=\prod_p\left(1-\frac{\mathbb{Y}(p)}{p}\right)^{-1}.

Define

C=15∏ℓ≥3ℓ prime∏i=2∞(1−1ℓi)\mathfrak{C}=15\prod_{\substack{\ell\geq 3\\ \ell\text{ prime}}}\prod_{i=2}^{\infty}\left(1-\frac{1}{\ell^i}\right)

and, for odd hh,

c(h)=∏pn∥h∏i=1n(1−1pi)−1.\mathfrak{c}(h)=\prod_{p^n\parallel h}\prod_{i=1}^n\left(1-\frac{1}{p^i}\right)^{-1}.

The refined Soundararajan conjecture. As h→∞h\to\infty through odd values,

F(h)∼C15c(h)h E(1L(1,Y)2log⁡(πh/L(1,Y)))∼Cc(h)hlog⁡(πh).\mathcal{F}(h)\sim\frac{\mathfrak{C}}{15}\mathfrak{c}(h)h\,\mathbb{E}\left(\frac{1}{L(1,\mathbb{Y})^2\log(\pi h/L(1,\mathbb{Y}))}\right)\sim\mathfrak{C}\mathfrak{c}(h)\frac{h}{\log(\pi h)}.

This refines Soundararajan's heuristic F(h)≍h/log⁡h\mathcal{F}(h)\asymp h/\log h and combines Cohen–Lenstra heuristics with the distribution of quadratic Dirichlet LL-values. The source presents it as conjectural; its resolution status is not specified here.

References

Primary source

Samuel Holmin, Nathan Jones, Pär Kurlberg, Cam McLeman and Kathleen L. Petersen, “Missing class groups and class number statistics for imaginary quadratic fields”, arXiv:1510.04387 (2015).

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