Bounds for the distribution of the Frobenius traces associated to a generic abelian variety (2207.02913v1)

Abstract: Let $g \geq 1$ be an integer and let $A$ be an abelian variety defined over $\mathbb{Q}$ and of dimension $g$. Assume that, for each sufficiently large prime $\ell$, the image of the residual modulo $\ell$ Galois representation of $A$ is isomorphic to $\text{GSp}{2g}(\mathbb{Z}/\ell\mathbb{Z})$. For an integer $t$ and a positive real number $x$, denote by $\pi_A(x, t)$ the number of primes $p \leq x$, of good reduction for $A$, for which the Frobenius trace $a{1, p}(A)$ associated to the reduction of $A$ modulo $p$ equals $t$. Assuming the Generalized Riemann Hypothesis for Dedekind zeta functions, we prove that $\pi_A(x, 0) \ll_A x^{1-\frac{1}{2g^2+g+1}}/(\log x)^{1-\frac{2}{2g^2+g+1}}$ and that $\pi_A(x, t) \ll_A x^{1-\frac{1}{2g^2+g+2}}/(\log x)^{1-\frac{2}{2g^2+g+2}}$ if $t \neq 0$. Under the assumptions stated above, we also prove the existence of a density one set of primes $p$ satisfying $|a_{1, p}(A)|> p^{\frac{1}{2g^2+g+1}}/(\log p)^{\varepsilon}$ for any fixed $\varepsilon>0$. Assuming, in addition to the Generalized Riemann Hypothesis for Dedekind zeta functions, Artin's Holomorphy Conjecture and a Pair Correlation Conjecture for Artin L-functions, we prove that $\pi_A(x, 0) \ll_A x^{1-\frac{1}{g+1}}/(\log x)^{1-\frac{4}{g+1}}$ and that $\pi_A(x, t) \ll_A x^{1-\frac{1}{g+2}}/(\log x)^{1-\frac{4}{g+2}}$ if $t \neq 0$, and we deduce the existence of a density one set of primes $p$ satisfying $|a_{1, p}(A)|> p^{\frac{1}{g+2}-\varepsilon}$ for any fixed $\varepsilon>0$. These are currently the best known conditional upper bounds for $\pi_A(x, t)$ and the best known conditional lower bounds for $|a_{1, p}(A)|$, for most primes $p$.