Upper and lower bounds on moments of quadratic character sums and theta functions

Abstract: In this note, we prove unconditional lower bounds for all integer moments of quadratic character sums in a wide range of parameters. Assuming the Generalised Riemann Hypothesis (GRH), we prove a sharp upper bound on integer moments of character sums of arbitrary length. We obtain similar results in the case of quadratic theta functions. Moreover, in this case we prove an unconditional upper bound for the second moment improving previous results of Louboutin and the author.