In this paper we introduce multiplicative Dirac structures on Lie groupoids, providing a unified framework to study both multiplicative Poisson bivectors (i.e., Poisson group(oid)s) and multiplicative closed 2-forms (e.g., symplectic groupoids). We prove that for every source simply connected Lie groupoid $G$ with Lie algebroid $AG$, there exists a one-to-one correspondence between multiplicative Dirac structures on $G$ and Dirac structures on $AG$, which are compatible with both the linear and algebroid structures of $AG$. We explain in what sense this extends the integration of Lie bialgebroids to Poisson groupoids carried out in \cite{ MX2} and the integration of Dirac manifolds of \cite{ BCWZ}. We also explain the connection between multiplicative Dirac structures and higher geometric structures such as $\mathcal{ LA}$-groupoids and $\mathcal{ CA}$-groupoids.
Categories: math.DG math.SG