2020/11/27 by Ashvin Swaminathan, Swaminathan, Ashvin · 2 citations
Mathematics · #11E76 (secondary) #11R29 #11R65 (primary) #Algebraic Geometry and Number Theory #FOS: Mathematics #Number Theory (math.NT) #and 11R45
paper · pdf · doi:10.48550/arxiv.2011.13578
openalex publication_date 2020/11/27 · openalex created_date 2022/07/25 · openalex updated_date 2026/07/28
We give a parametrization of square roots of the ideal class of the inverse different of rings defined by binary forms in terms of the orbits of a coregular representation. This parametrization, which can be construed as a new integral model of a ``higher composition law'' discovered by Bhargava and generalized by Wood, was the missing ingredient needed to solve a range of previously intractable open problems concerning distributions of class groups, Selmer groups, and related objects. For instance, in this paper, we apply the parametrization to bound the average size of the 2-class group in families of number fields defined by binary n-ic forms, where n ≥ 3 is an arbitrary integer, odd or even; in the paper [41], we applied it to prove that most integral odd-degree binary forms fail to primitively represent a square; and in the paper [11], joint with Bhargava and Shankar, we applied it to bound the second moment of the size of the 2-Selmer group of elliptic curves.