Character analogues of Cohen type identities and related Voronoi summation formulas

TL;DR

This paper extends Cohen-type identities and Voronoi summation formulas to character analogues, deriving new identities involving twisted divisor sums, Bessel functions, and establishing positivity of certain L-values.

Contribution

It introduces novel identities for weighted divisor functions related to Dirichlet characters and provides new expressions for L(1, χ), including positivity results.

Findings

Derived Cohen-type identities for twisted divisor sums

Established Voronoi-type summation formulas for these identities

Provided a new expression for L(1, χ) confirming its positivity

Abstract

In \cite{MR2221114}, B.~C.~Berndt and A.~Zaharescu introduced the twisted divisor sums associated with the Dirichlet character while studying the Ramanujan's type identity involving finite trigonometric sums and doubly infinite series of Bessel functions. Later, in a follow-up paper \cite{MR3541702}, S. Kim extended the definition of the twisted divisor sums to twisted sums of divisor functions. In this paper, we derive identities associated with the aforementioned weighted divisor functions and the modified $K$-Bessel function in light of recent results obtained by the first author and B. Maji \cite{ debika2023}. Moreover, we provide a new expression for $L(1, \chi)$ from which we establish the positivity of $L(1, \chi)$ for any real primitive character $\chi$. In addition, we deduce Cohen-type identities and then exhibit the Vorono\"i-type summation formulas for them.