Cohen-Lenstra-Martinet density heuristics for elementary abelian 2- and 3-extensions

Let tt be a positive integer, let pp be an odd prime in the degree-22 case, and let p5p\geq 5 be prime in the degree-33 case. Write (p)=k1(1pk)(p)_\infty=\prod_{k\geq1}(1-p^{-k}) and (p)1=1p1(p)_1=1-p^{-1}, and analogously (p2)=k1(1p2k)(p^2)_\infty=\prod_{k\geq1}(1-p^{-2k}) and (p2)1=1p2(p^2)_1=1-p^{-2}. Cohen-Lenstra-Martinet heuristic. If K=Q(d1,,dt)K=\mathbb{Q}(\sqrt{d_1},\ldots,\sqrt{d_t}), then

Prob(phK)=((p)(p)1)2t1.\mathrm{Prob}(p\nmid h_K)=\left(\frac{(p)_\infty}{(p)_1}\right)^{2^t-1}.

If KK has degree 3t3^t and is the compositum of tt cyclic cubic fields, then

Prob(phK)={((p)(p)1)2(3t1)/2,p1(mod3),((p2)(p2)1)(3t1)/2,p2(mod3).\mathrm{Prob}(p\nmid h_K)= \begin{cases} \left(\dfrac{(p)_\infty}{(p)_1}\right)^{2(3^t-1)/2},&p\equiv1\pmod3,\\ \left(\dfrac{(p^2)_\infty}{(p^2)_1}\right)^{(3^t-1)/2},&p\equiv2\pmod3. \end{cases}

These are heuristic predictions obtained by treating the class groups of intermediate cyclic prime-degree fields as independent. The source does not state a resolution.

Sources & referencesView supporting material

Primary source

Razvan Barbulescu and Jishnu Ray, “Numerical verification of the Cohen-Lenstra-Martinet heuristics and of Greenberg's p-rationality conjecture”, arXiv:1706.04847 (2019).

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