Improved explicit Burgess-strength bounds for composite moduli

Source abstract

Consider the character sum $S(M,N)=\sum_{n=M+1}^{M+N}χ(n)$ for a non-principal Dirichlet character $χ(n)$ to a (possibly composite) modulus $q$. Burgess proved that $S(M,N)\ll N^{1/2}q^{3/16+\varepsilon}$, for any $\varepsilon>0$. This was made explicit by Jain-Sharma et al., but only for moduli $q\geq \exp(\exp(9.594))\approx 8.03\times 10^{6373}$. We prove a stronger result that holds when $q\geq 1.627\times 10^{19}$.