Fundamental group of moduli of principal bundles on curves

Abstract

Let $X$ be a compact connected Riemann surface of genus at least two, and let ${G}$ be a connected semisimple affine algebraic group defined over $\mathbb C$. For any $\delta \in \pi_1({G})$, we prove that the moduli space of semistable principal ${G}$--bundles over $X$ of topological type $\delta$ is simply connected. In contrast, the fundamental group of the moduli stack of principal ${G}$--bundles over $X$ of topological type $\delta$ is shown to be isomorphic to $H^1(X, \pi_1({G}))$.