Effective Convergence Bounds for Frobenius Structures on Connections
Let be a fixed algebraic variety defined by polynomials in variables with integer coefficients. We show that there exists a constant such that for almost all primes for all but at most points on the reduction of modulo at least one of the components has a large multiplicative order. This generalises several previous results and is a step towards a conjecture of B. Poonen.
Let be an absolutely simple abelian variety over a number field; we study whether the reductions tend to be simple, too. We show that if is a definite quaternion algebra, then the reduction is geometrically isogenous to the self-product of an absolutely simple abelian variety for in a set of positive density, while if is of Mumford type, then is simple for almost all . For a large class of abelian varieties with commutative absolute endomorphism ring, we give an explicit upper bound...