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

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

Define

C=153 primei=2(11i)\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)=pnhi=1n(11pi)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 hh\to\infty through odd values,

F(h)C15c(h)hE(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/logh\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.

Sources & referencesView supporting material

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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