Étale metaplectic covers of reductive group schemes

Abstract

Given a reductive group scheme $G$, we give a linear algebraic description of reduced étale $4$-cocycles on its classifying stack $\mathrm{B}(G)$. These cocycles form a $2$-groupoid, which we interpret as parameters of metaplectic covers of $G$. We use our linear algebraic description to define the Langlands dual of a metaplectic cover.

arXiv comment78 pages, a substantial revision of "metaplectic group schemes"