On the $p$-ranks of class groups of certain Galois extensions

Abstract: Let $p$ be an odd prime, let $N$ be a prime with $N \equiv 1 \pmod{p}$, and let $\zeta_p$ be a primitive $p$-th root of unity. We study the $p$-rank of the class group of $\mathbb{Q}(\zeta_p, N^{1/p})$ using Galois cohomological methods and obtain an exact formula for the $p$-rank in terms of the dimensions of certain Selmer groups. Using our formula, we provide a numerical criterion to establish upper and lower bounds for the $p$-rank, analogous to the numerical criteria provided by F.~Calegari--M.~Emerton and K.~Schaefer--E.~Stubley for the $p$-ranks of the class group of $\mathbb{Q}(N^{1/p})$. In the case $p=3$, we use Redei matrices to provide a numerical criterion to exactly calculate the $3$-rank, and also study the distribution of the $3$-ranks as $N$ varies through primes which are $4,7 \pmod{9}$. This is joint work with Ufuoma Asenhesa, Rusiru Gambheera, Enrique Nunez Lon-Wo, and Arshay Sheth.

commutative algebraalgebraic geometrygroup theorynumber theoryrings and algebrasrepresentation theory

Audience: researchers in the topic

Calgary Algebra and Number Theory Seminar

Series comments: This seminar series is partially supported by the Pacific Institute for the Mathematical Sciences (PIMS).