Strong ergodicity for the Gamma-jump operator and for actions of Polish wreath products

Abstract

Let $\Gamma$ and $\Delta$ be sufficiently distinct countable groups. We show that there is an orbit equivalence relation $E$, induced by an action of the Polish wreath product group $\Gamma\wr\Gamma$, so that $E$ is generically $F$-ergodic for any orbit equivalence relation $F$ induced by an action of $\Delta\wr\Delta$. More generally, we establish generic ergodicity between $\Gamma$-jumps and the iterated $\Delta$-jumps, answering a question of Clemens and Coskey. The proofs follow a translation between Borel homomorphisms and definable pins.