Explicit Burgess inequalities for cubefree moduli
Elchin Hasanalizade, Hua Lin, Greg Martin, Andradis Luna Martínez, Enrique Treviño
TL;DR
This paper proves explicit Burgess-type bounds for Dirichlet character sums modulo cubefree moduli, extending beyond prime moduli to composite ones. The authors establish an explicit Weil-type inequality for short, shifted character sums and embed it in a general inductive framework to bound $|S_{\chi}(M,N)|$; they carefully choose and bound auxiliary parameters through a detailed analysis of $v_{\mathcal{A}}(x)$ sums and related arithmetic sums. The main contributions are an improved explicit constant for $r=2$ and explicit Burgess bounds for all $r\ge3$ when $q$ is cubefree, with the constants $C(r)$ and $D(r)$ computed (and tabulated) and two bound families $T_1(q)$ and $T_2(q)$ defined. These results provide practically usable explicit estimates for composite moduli, with potential applications to least $k$-th power residues, $L$-value bounds, and related analytic-number-theory problems.
Abstract
Burgess proved that for $χ_q$ a primitive Dirichlet character modulo $q$ with $q$ cubefree, $\Big|\sum_{M< n\le M+N}χ_q(n)\Big| \ll N^{1-\frac{1}{r}}q^{\frac{r+1}{4r^2}+ε}$ for all integers $r\ge1.$ More recently, explicit versions with prime moduli $q$ were computed by Booker, McGown, Treviño, and Francis, with applications to finding the least $k$-th power residue, and bounding the size of Dirichlet $L$-functions just to name a few. Jain-Sharma, Khale, and Liu proved an explicit estimate for $r=2.$ We improve their explicit constant for $r = 2$ and compute an explicit Burgess bound for cubefree $q$ for $r\ge 3$.
