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Jacobian varieties with group algebra decomposition not affordable by Prym varieties

Algebraic Geometry 2024-09-23 v1

Abstract

The action of a finite group GG on a compact Riemann surface XX naturally induces another action of GG on its Jacobian variety J(X)\operatorname{J}(X). In many cases, each component of the group algebra decomposition of J(X)\operatorname{J}(X) is isogenous to a Prym varieties of an intermediate covering of the Galois covering πG ⁣:XX/G\pi_G\colon X \to X/G; in such a case, we say that the group algebra decomposition is affordable by Prym varieties. In this article, we present an infinite family of groups that act on Riemann surfaces in a manner that the group algebra decomposition of J(X)\operatorname{J}(X) is not affordable by Prym varieties; namely, affine groups Aff(Fq)\operatorname{Aff}(\mathbb{F}_q) with some exceptions: q=2q = 2, q=9q = 9, qq a Fermat prime, q=2nq = 2^n with 2n12^n-1 a Mersenne prime and some particular cases when X/GX/G has genus 00 or 11. In each one of this exceptional cases, we give the group algebra decomposition of J(X)\operatorname{J}(X) by Prym varieties.

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Cite

@article{arxiv.2402.17998,
  title  = {Jacobian varieties with group algebra decomposition not affordable by Prym varieties},
  author = {Benjamín Moraga},
  journal= {arXiv preprint arXiv:2402.17998},
  year   = {2024}
}

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14 pages