Hurwitz correspondences on compactifications of $\mathcal{M}_{0,N}$

Abstract

Hurwitz correspondences are certain multivalued self-maps of the moduli space $\mathcal{M}_{0,N}$. They arise in the study of Thurston's topological characterization of rational functions. We consider the dynamics of Hurwitz correspondences and ask: On which compactifications of $\mathcal{M}_{0,N}$ should they be studied? We compare a Hurwitz correspondence $\mathcal{H}$ across various modular compactifications of $\mathcal{M}_{0,N}$, and find a weighted stable curves compactification $X_N^\dagger$ that is optimal for its dynamics. We use $X_N^\dagger$ to show that the $k$th dynamical degree of $\mathcal{H}$ is the absolute value of the dominant eigenvalue of the pushforward induced by $\mathcal{H}$ on a natural quotient of $H_{2k}(\overline{\mathcal{M}}_{0,N})$.