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Root Numbers of 5-adic Curves of Genus Two Having Maximal Ramification

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Abstract

The formulas for local root numbers of abelian varieties of dimension one are known. In this paper we treat the simplest unknown case in dimension two by considering a curve of genus 2 defined over a 5-adic field such that the inertia acts on the first \(\ell \)-adic cohomology group through the largest possible finite quotient, isomorphic to \(C_5\rtimes C_8\). We give a few criteria to identify such curves and prove a formula for their local root numbers in terms of invariants associated to a Weierstrass equation.

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Notes

  1. The formula is stated for the \(\epsilon _0\)-factor of \(\chi \), which is equal to the \(\epsilon \)-factor when \(\chi \) is ramified.

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Acknowledgements

I thank my doctoral thesis advisors Adriano Marmora and Rutger Noot as well as Kȩstutis Česnavičius and Takeshi Saito for their remarks and suggestions concerning the manuscript. I also thank Jeff Yelton for answering my questions about his results on the splitting fields of the 4-torsion of Jacobians. The study presented in this paper constitutes a part of my thesis.

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Correspondence to Lukas Melninkas.

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Melninkas, L. Root Numbers of 5-adic Curves of Genus Two Having Maximal Ramification. Milan J. Math. 91, 255–279 (2023). https://doi.org/10.1007/s00032-023-00380-7

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