The Cohen–Lenstra–Martinet heuristic for Arakelov class groups

Let KK be a number field, let Kˉ\bar K be an algebraic closure, let GG be a finite group, let PP be a set of primes, and let VV be the prescribed rational GG-module. Let Λ=Z(P)[G]\Lambda=\Z_{(P)}[G], let \cF\cF be the infinite family of pairs (F,i)(F,i) described in the setup, and for B>0B>0 let \cFcB\cF_{c\leq B} be the subfamily with ramification norm at most BB. For a reasonable function ff on the corresponding module-isomorphism space, write \bE\cMV(f)\bE_{\cM_V}(f) for its expected value.

Cohen–Lenstra–Martinet conjecture. If PP is finite, then

limB(F,i)\cFcBf(ΛZ[G]\ArF)#\cFcB=\bE\cMV(f).\lim_{B\to\infty}\frac{\sum_{(F,i)\in\cF_{c\leq B}}f(\Lambda\otimes_{\Z[G]}\Ar_F)}{\#\cF_{c\leq B}}=\bE_{\cM_V}(f).

This is a refined distributional conjecture for Arakelov class groups in families of Galois extensions, proposed in the cited work as a version of the Cohen–Lenstra–Martinet heuristics. The supplied text does not give a resolution status.

Sources & referencesView supporting material

Primary source

Alex Bartel, Henri Johnston and Hendrik W. Lenstra, “Arakelov class groups of random number fields”, arXiv:2005.11533 (2024).

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