Relational symplectic groupoids and Poisson sigma models with boundary

Abstract: We introduce the notion of relational symplectic groupoid as a way to integrate Poisson manifolds in general, following the construction through the Poisson sigma model (PSM) given by Cattaneo and Felder. We extend such construction to the infinite dimensional setting, where we are able to describe the relational symplectic groupoid in terms of immersed Lagrangian Bannach submanifolds. This corresponds to a groupoid object in the "extended symplectic category" and it can be related to the ususal version of symplectic groupoids via reduction. We prove the existence of such an object for any Poisson manifold and the uniqueness of a compatible Poisson structure on the base, for a special type of relational symplectic groupoids. We develop the notion of equivalence, that allows us to compare finite and infinite dimensional examples. We discuss some other extensions to different categories, where the relational construction still make sense, in an effort to understand better geometric quantization of symplectic manifolds in this new perspective.