Cocycle Relations and Elliptic Gamma Values

Source abstract

In the recent work of Bergeron-Charollois-García \cite{BCG23}, a conjectural analytic expression for elliptic units for complex cubic fields was proposed: namely, as the value of a smoothed quotient of elliptic Gamma functions. The complex number depended on the conductor ideal, ray class group element, smoothing ideal, and a `torsion point' $h$. If this analytic function is to fit into the framework of explicit class field theory, then, as in the case of torsion points on CM elliptic curves, our choice of $h$ should only depend on its congruence class modulo some lattice $L$. This conjecture has been supported by much numerical evidence. In this paper, we use the cocycle relations satisfied by the smoothed elliptic Gamma function to prove that the construction is indeed independent of $h$.