Multipliers and Lacunary Sets in Non-Amenable Groups
Multipliers and Lacunary Sets in Non-Amenable Groups
Let $G$ be a discrete group. Let $\lambda : G \to B(\ell_2(G),\ell_2(G))$ be the left regular representation. A function $\ph : G \to \comp$ is called a completely bounded multiplier (= Herz-Schur multiplier) if the transformation defined on the linear span $K(G)$ of $\{\lambda(x),x \in G\}$ by $$\sum_{x \in G} …