Fractional Moments of Dirichlet $L$-Functions

Abstract

Let $k$ be a positive real number, and let $M_k(q)$ be the sum of $|L(\tfrac12,\chi)|^{2k}$ over all non-principal characters to a given modulus $q$. We prove that $M_k(q)\ll_k \phi(q)(\log q)^{k^2}$ whenever $k$ is the reciprocal $n^{-1}$ of a positive integer $n$. If one assumes the Generalized Riemann Hypothesis then the estimate holds for all positive real $k<2$.