Multiplicative forms on Poisson groupoids

Abstract

Given a Lie groupoid $\mathcal{G}$ over $M$, $A$ the tangent Lie algebroid of $\mathcal{G}$, and $\rho: A\rightarrow TM$ the anchor map, we provide a formula that decomposes an arbitrary multiplicative $k$-form $\Theta$ on $\mathcal{G}$ into two parts. The first part is $e$, a $1$-cocycle of $\mathfrak{J}\mathcal{G}$ valued in $\wedge^k T^*M$, and the second part is $\theta\in \Gamma(A^*\otimes (\wedge^{k-1} T^*M))$ which is $\rho$-compatible, meaning that $\iota_{\rho(u)}\theta(u)=0$ for all $u\in A$. We call this pair of data $(e,\theta)$ the $(0,k)$-characteristic pair of $\Theta$. Next, we prove that if $\mathcal{G}$ is a Poisson Lie groupoid, then the space $\Omega^{\bullet}_{\mathrm{mult}}(\mathcal{G})$ of multiplicative forms on $\mathcal{G}$ has a differential graded Lie algebra (DGLA) structure. Furthermore, when combined with $\Omega^\bullet(M)$, which is the space of forms on the base manifold $M$, $\Omega^{\bullet}_{\mathrm{mult}}(\mathcal{G})$ forms a canonical DGLA crossed module. This supplements a previously known fact that multiplicative multivector fields on $\mathcal{G}$ form a DGLA crossed module with the Schouten algebra $\Gamma(\wedge^\bullet A)$ stemming from the tangent Lie algebroid $A$.