Covariant derivatives in the representation-valued Bott-Shulman-Stasheff and Weil complex

Abstract

For a Lie groupoid $G$, the differential forms on its nerve comprise a double complex. A natural question is if this statement extends to forms with values in a representation $V$ of $G$. In this paper, we research two types of covariant derivatives which commute with the simplicial differential, yielding two types of "curved" double complexes of forms with coefficients in $V$. The naive approach is to consider a linear connection $\nabla$ on $V$, in which case $d^\nabla$ commutes with the simplicial differential if and only if $\nabla$ satisfies a certain (restrictive) invariance condition. The heart of this paper focuses on another, more compelling approach: using a multiplicative Ehresmann connection for a bundle of ideals. In this case, we obtain a geometrically richer curved double complex, where the cochain map is given by the horizontal exterior covariant derivative $D$, which generalizes the well-known operator from the theory of principal bundles. Moreover, both differential operators $d^\nabla$ and $D$ are researched in the infinitesimal setting of Lie algebroids, as well as their relationship with the van Est map. We conclude by using the operator $D$ to study the curvature of an (infinitesimal) multiplicative Ehresmann connection.