Let $A$ be a $g$-dimensional abelian variety over $\mathbb{ Q}$ whose adelic Galois representation has open image in $\text{ GSp}_{ 2g} \widehat{ \mathbb{ Z}}$. We investigate the endomorphism algebras $\text{ End}(A_p) \otimes \mathbb{ Q} = \mathbb{ Q}( \pi_p )$ of the reduction of $A$ modulo primes $p$ at which this reduction is ordinary and simple. We obtain conditional and unconditional asymptotic upper bounds on the number of primes at which this "Frobenius field" is a specified number field and, when $A$ is two-dimensional, at which the Frobenius field contains a specified real quadratic number field. These investigations continue the investigations of variants of the Lang-Trotter Conjectures on elliptic curves.
Categories: math.NT