Moduli of flat connections on smooth varieties

Abstract

We study the moduli functor of flat bundles on smooth, possibly non-proper, algebraic variety $X$ (over a field of characteristic zero). For this we introduce the notion of \emph{formal boundary} of $X$, denoted by $\partial X$, which is a formal analogue of the boundary at infinity of the Betti topological space associated to $X$. We explain how to construct two derived moduli functors $Vec{t}^{\nabla }(X)$ and $Vec{t}^{\nabla }(\partial X)$, of flat bundles on $X$ and on $\partial X$, as well as a restriction map $R:Vec{t}^{\nabla }(X)\to Vec{t}^{\nabla }(\partial X)$ from the former to the later. This work contains two main results. First we prove that the morphism R comes equipped with a canonical shifted Lagrangian structure in the sense of [PTVV]. This first result can be understood as the de Rham analogue of the existence of Poisson structures on moduli of local systems previously studied by the authors. As a second statement, we prove that the geometric fibers of $R$ are representable by "quasi-algebraic spaces", a slight weakening of the notion of algebraic spaces.

60 pages, final version