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Frobenius Distribution for Quotients of Fermat Curves of Prime Exponent
Published online by Cambridge University Press: 20 November 2018
Abstract
Let
$C$
denote the Fermat curve over
$\mathbb{Q}$
of prime exponent
$l$
. The Jacobian
$\text{Jac(}C\text{)}$
of
$C$
splits over
$\mathbb{Q}$
as the product of Jacobians
$\text{Jac(}{{C}_{k}})$
,
$1\,\le \,k\,\le \,\ell \,-\text{2}$
, where
${{C}_{k}}$
are curves obtained as quotients of
$C$
by certain subgroups of automorphisms of
$C$
. It is well known that
$\text{Jac(}{{C}_{k}}\text{)}$
is the power of an absolutely simple abelian variety
${{B}_{k}}$
with complex multiplication. We call degenerate those pairs
$(l,\,k)$
for which
${{B}_{k}}$
has degenerate
$\text{CM}$
type. For a non-degenerate pair
$(l,\,k)$
, we compute the Sato–Tate group of
$\text{Jac(}{{C}_{k}}\text{)}$
, prove the generalized Sato–Tate Conjecture for it, and give an explicit method to compute the moments and measures of the involved distributions. Regardless of whether
$(l,\,k)$
is degenerate, we also obtain Frobenius equidistribution results for primes of certain residue degrees in the
$l$
-th cyclotomic field. Key to our results is a detailed study of the rank of certain generalized Demjanenko matrices.
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- Copyright
- Copyright © Canadian Mathematical Society 2016
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