Some classes of smooth bimodules over II$_1$ factors and their associated 1-cohomology spaces (2304.06242v3)

Abstract: We study several classes of Banach bimodules over a II$_1$ factor $M$, endowed with topologies that make them "smooth" with respect to $L^p$-norms implemented by the trace on $M$. Letting $M\subset \B= \B(L^2M)$, and $2\leq p < \infty$, we consider: $(1)$ the space $\B(p)$, obtained as the completion of $\B$ in the norm [ \vertiii{T}_p := \sup {|\varphi(T)| \mid \varphi \in \B^*, \sup{|\varphi(xYz)| \mid Y\in (\B)_1, x, z \in M\cap (L^pM)_1} \leq 1 }; ] $(2)$ the subspace $\K(p)\subset \B(p)$, obtained as the closure in $\B(p)$ of the space of compact operators $\K(L^2M)$; $(3)$ the space $\K_p\subset \B$ of operators that are $\vertiii{ \, \cdot \, }_p$-limits of bounded sequences of operators in $\K(L^2M)$. We prove that $\K_p$ are all equal to the {\it $\tau$-rank-completion} of $\K(L^2M)$ in $\B$, defined by \begin{align} \text{\rm q}\K_M:= {K\in \B(L^2M) \mid & \exists K_n \in \K(L^2M), p_n\in \mathcal P(M), \nonumber \ & \lim_n |p_n(K-K_n)p_n|= 0, \lim_n\tau(1-p_n)=0}. \nonumber \end{align} We show that any separable II$_1$ factor $M$ admits non-inner derivations into $\text{\rm q}\K_M$, but that any derivation $\delta:M \rightarrow \text{\rm q}\K_M$ is a pointwise limit in $\tau$-rank-metric of inner derivations.