On the deck groups of iterates of bicritical rational maps

Abstract: Given a rational map $f:\widehat{\mathbb C}\to\widehat{\mathbb C}$ on the Riemann sphere, we define $\mathrm{Deck}(f)$ to be the group of M\"obius transformations $\mu$ satisfying $f \circ \mu = f$. In this note, we consider the groups $\mathrm{Deck}(f<sup>k)$, where $f$ is a \emph{bicritical} rational map (that is, a rational map with exactly two critical points) and $f<sup>k$ denotes the $k$th iterate of $f$. In particular, we give a complete description of which groups (up to isomorphism) arise as the groups $\mathrm{Deck}(f<sup>k)$ for bicritical rational maps $f$.