A property for locally convex ${}^{\ast }$-algebras related to Property $(T)$ and character amenability

For a locally convex ${}^{\ast }$-algebra $A$ equipped with a fixed continuous ${}^{\ast }$-character $\epsilon$, we define a cohomological property, called property $(FH)$, which is similar to character amenability. Let $C_c(G)$ be the space of continuous functions on a second countable locally compact group $G$ with compact supports, equipped with the convolution ${}^{\ast }$-algebra structure and a certain inductive topology. We show that $(C_c(G),{\epsilon }_G)$ has property $(FH)$ if and only if $G$ has property $(T)$. On the other hand, many Banach algebras equipped with canonical characters have property $(FH)$ (e.g., those defined by a nice locally compact quantum group). Furthermore, through our studies on both property $(FH)$ and character amenablility, we obtain characterizations of property $(T)$, amenability and compactness of $G$ in terms of the vanishing of one-sided cohomology of certain topological algebras, as well as in terms of fixed point properties. These characterizations can be regarded as analogues of one another. Moreover, we show that $G$ is compact if and only if the normed algebra $\{f\in C_c(G):{\int }_{G}f(t)dt=0\}$ (under $\mathrm{\parallel }\cdot {\mathrm{\parallel }}_{L^1(G)}$) admits a bounded approximate identity with the supports of all its elements being contained in a common compact set.