On the reduced space of multiplicative multivectors

Abstract: A strict Lie $2$-algebra $\Gamma(\wedge^\bullet A) \stackrel{T}{\rightarrow} \mathfrak{X}{\mathrm{mult}}^\bullet(\mathcal{G})$ is associated with any Lie groupoid $\mathcal{G}$. Here, $\Gamma(\wedge^\bullet A)$ is the Schouten algebra of the tangent Lie algebroid $A$ of $\mathcal{G}$ and $\mathfrak{X}{\mathrm{mult}}^\bullet(\mathcal{G})$ is the space of multiplicative multivectors on $\mathcal{G}$. The quotient ${R}{\mathrm{mult}}^\bullet:=\mathfrak{X}{\mathrm{mult}}^\bullet(\mathcal{G})/\mathrm{Img} T$, a Morita invariant of $\mathcal{G}$, is called the reduced space of multiplicative multivectors. We prove a canonical decomposition formula of elements in $\mathfrak{X}{\mathrm{mult}}^\bullet(\mathcal{G})$ and establish a key relation between ${R}{\mathrm{mult}}^k$ and the cohomology $\mathrm{H} ^1(\mathfrak{J} \mathcal{G},\wedge^k A)$ where $\mathfrak{J} \mathcal{G}$ is the jet groupoid of $\mathcal{G}$ and $1\leqslant k\leqslant \mathrm{rank} A$. We also study ${R}{\mathrm{diff}}^\bullet $, the reduced space of Lie algebroid differentials on $A$. By taking infinitesimals, $\bar{\delta}: $ ${R}{\mathrm{mult}}^\bullet $ $\to $ ${R}_{\mathrm{diff}}^\bullet $, the two reduced spaces are related. We find that the kernel of $\bar{\delta}$ is isomorphic to the kernel of the Van Est map $\mathrm{H}^1(\mathcal{G},\wedge^k \ker\rho)\to \mathrm{H}^1(A,\wedge^k \ker\rho)$, where $\rho$ is the anchor of $A$.