On the effective cone of higher codimension cycles in ${\overline{\mathcal{M}}}_{g,n}$

Abstract

We exhibit infinitely many extremal effective codimension-$k$ cycles in ${\overline{\mathcal{M}}}_{g,n}$ in the cases $g\ge 3,n\ge g-1$ and $k=2$, $g\ge 2$, $k\le n-g,g,$ and $g=1$, $k\le n-2$. Hence in these cases the effective cone is not rational polyhedral.

arXiv comment22 pages