Non-polyhedral effective cones from the moduli space of curves

Abstract

We show that the pseudoeffective cone of divisors $\overline{\text{Eff}}^1(\overline{\mathcal{M}}_{g,n})$ for $g\geq 2$ and $n\geq 2$ is not polyhedral by showing that the class of the fibre of the morphism forgetting one point forms an extremal round edge of the dual nef cone of curves $\overline{\text{Nef}}_1(\overline{\mathcal{M}}_{g,n})$.