Arithmetic of Hecke L-functions of quadratic extensions of totally real fields

Abstract

Deep work by Shintani in the 1970's describes Hecke $L$-functions associated to narrow ray class group characters of totally real fields $F$ in terms of what are now known as Shintani zeta functions. However, for $[F:\mathbb{Q}] = n \geq 3$, Shintani's method was ineffective due to its crucial dependence on abstract fundamental domains for the action of totally positive units of $F$ on $\mathbb{R}^n_+$, so-called $\textit{Shintani sets}$. These difficulties were recently resolved in independent work of Charollois, Dasgupta, and Greenberg and Diaz y Diaz and Friedman. For those narrow ray class group characters whose conductor is an inert rational prime in a totally real field $F$ with narrow class number $1$, we obtain a natural combinatorial description of these sets, allowing us to obtain a simple description of the associated Hecke $L$-functions. As a consequence, we generalize earlier work of Girstmair, Hirzebruch, and Zagier, that offer combinatorial class number formulas for imaginary quadratic fields, to real and imaginary quadratic extensions of totally real number fields $F$ with narrow class number $1$. For CM quadratic extensions of $F$, our work may be viewed as an effective affirmative answer to Hecke's Conjecture that the relative class number has an elementary arithmetic expression in terms of the relative discriminant.