Admissible covers and stable maps

Abstract

Moduli spaces of admissible covers and stable maps of target curves give rise to cycles on ${\overline{M}}_{g,n}$. We prove a formula relating these cycles. It recovers both the Ekedahl-Lando-Shapiro-Vainshtein formula and the Gromov-Witten/Hurwitz correspondence, providing a cycle-theoretic refinement thereof. The formula is verified computationally in low-genus cases with the help of Johannes Schmitt.

32 pages, Appendix by Johannes Schmitt