Positive density of primes of ordinary reduction for abelian varieties of simple signature

By a result of Serre, if $A$ is an elliptic curve without CM defined over a number field $L$, then the set of primes of $L$ for which $A$ has ordinary reduction has density $1$. Katz and Ogus proved the same is true when $A$ is an abelian surface, after possibly passing to a finite extension of $L$. More recently, Sawin computed the density of the set of primes of $L$ for which an abelian surface $A$ has ordinary reduction, depending on the endomorphism algebra of $A$. In this paper, we prove some generalizations of these results when $A$ is an absolutely simple abelian variety of arbitrary dimension whose endomorphism algebra is a CM field $F$, under specific conditions on the signature of the multiplication action of $F$ on $A$. We include explicit examples from Jacobians of curves of genus three through seven admitting cyclic covers to the projective line.

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ArXiv.org
Published
2025-08-15
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Pregnancy and preeclampsia studies
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article

Positive density of primes of ordinary reduction for abelian varieties of simple signature

ArXiv.org
Pregnancy and preeclampsia studies
article

Positive density of primes of ordinary reduction for abelian varieties of simple signature

article en

Abstract

By a result of Serre, if $A$ is an elliptic curve without CM defined over a number field $L$, then the set of primes of $L$ for which $A$ has ordinary reduction has density $1$. Katz and Ogus proved the same is true when $A$ is an abelian surface, after possibly passing to a finite extension of $L$. More recently, Sawin computed the density of the set of primes of $L$ for which an abelian surface $A$ has ordinary reduction, depending on the endomorphism algebra of $A$. In this paper, we prove some generalizations of these results when $A$ is an absolutely simple abelian variety of arbitrary dimension whose endomorphism algebra is a CM field $F$, under specific conditions on the signature of the multiplication action of $F$ on $A$. We include explicit examples from Jacobians of curves of genus three through seven admitting cyclic covers to the projective line.

ArXiv.org
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Pregnancy and preeclampsia studies
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Positive density of primes of ordinary reduction for abelian varieties of simple signature · ArXiv.org (2025) | TGRS Research Map | TGRS