The automorphism group of M̄g,n

Abstract

Let \bar{\mathcal{M}}_{g,n}$ be the moduli stack parametrizing Deligne-Mumford stable n-pointed genus g curves and let \bar{M}_{g,n} be its coarse moduli space: the Deligne-Mumford compactification of the moduli space of n-pointed genus g smooth curves. We prove that the automorphisms groups of \bar{\mathcal{M}}_{g,n} and \bar{M}_{g,n} are isomorphic to the symmetric group on n elements S_{n} for any g,n such that 2g-2+n\geq 3, and compute the remaining cases.