Property T of group homomorphisms

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Abstract

In this article, we define and study property T for continuous homomorphisms between topological groups. If G is a locally compact group, we show that λG:GU(L2(G)) has property T if and only if either G is compact or G is non-amenable. Moreover, the abelianization Gab:=G/[G,G] is compact if and only if every continuous homomorphism from G to any abelian topological group has property T. Moreover, we show that G has property (T,FD) if and only if any continuous homomorphism from G to any compact group has property T. In the case when G is almost connected, the above is also equivalent to the canonical map from G to its Bohr compactification being a quotient map. We also give some new equivalent forms of the strong property T of a locally compact group. As a consequence, if G is a second countable and has strong property T and H is a closed subgroup of G, there exist at most one G-invariant mean on G/H.

Keywords

Locally compact groups
Property T
Strong property T

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This work is supported by the National Natural Science Foundation of China (11071126 and 11471168).