Paper detail

Permanence properties of property A and coarse embeddability for locally compact groups

If $H$ is a lattice in a locally compact second countable group $G$, then we show that $G$ has property A (respectively is coarsely embeddable into Hilbert space) if and only if $H$ has property A (respectively is coarsely embeddable into Hilbert space). Moreover, we show three interesting generalizations of this result. If $H$ is a closed subgroup of $G$ that is co-amenable in $G$, and if $H$ has property A (respectively, is coarsely embeddable into Hilbert space), then we show that $G$ has property A (respectively, is coarsely embeddable into Hilbert space). We also show that an extension of property A groups still has property A. On the coarse embeddability side, we show that if $\{e\}\rightarrow H\rightarrow G\rightarrow Q\rightarrow\{e\}$ is a short exact sequence, and if either $H$ is coarsely embeddable into Hilbert space and $Q$ has property A, or $H$ is compact and $Q$ is coarsely embeddable into Hilbert space, then $G$ is coarsely embeddable into Hilbert space. We extend the theory of measure equivalence to locally compact non-unimodular groups. In a natural way, we can also define measure equivalence subgroups. We show that property A and uniform embeddability into Hilbert space pass to measure equivalence subgroups. Using the same techniques, we show that also the Haagerup property, weak amenability and the weak Haagerup property pass to measure equivalence subgroups.