On equivalence relations induced by Polish groups admitting compatible two-sided invariant metrics

Abstract

Given a Polish group $G$, let $E(G)$ be the right coset equivalence relation $G^{\omega }/c(G)$, where $c(G)$ is the group of all convergent sequences in $G$. We first established two results: (1) Let $G,H$ be two Polish groups. If $H$ is TSI but $G$ is not, then $E(G)/{\le }_{B}E(H)$. (2) Let $G$ be a Polish group. Then the following are equivalent: (a) $G$ is TSI non-archimedean; (b)$E(G){\le }_B{E}_0^{\omega }$; and (c) $E(G){\le }_B{\mathbb{R}}^{\omega }/c_0$. In particular, $E(G){\sim }_B{E}_0^{\omega }$ iff $G$ is TSI uncountable non-archimedean. A critical theorem presented in this article is as follows: Let $G$ be a TSI Polish group, and let $H$ be a closed subgroup of the product of a sequence of TSI strongly NSS Polish groups. If $E(G){\le }_{B}E(H)$, then there exists a continuous homomorphism $S:G_0\to H$ such that $\ker (S)$ is non-archimedean, where $G_0$ is the connected component of the identity of $G$. The converse holds if $G$ is connected, $S(G)$ is closed in $H$, and the interval $[0,1]$ can be embedded into $H$. As its applications, we prove several Rigid theorems for TSI Lie groups, locally compact Polish groups, separable Banach spaces, and separable Fréchet spaces, respectively.

38 pages