Interpolation for intersections of Hardy-type spaces
Let $(X,μ)$ be a space with a finite measure $μ$, let $A$ and $B$ be $w^*$-closed subalgebras of $L^{\infty}(μ)$, and let $C$ and $D$ be closed subspaces of $L^p(μ)$ ($1<p<\infty$) that are modules over $A$ and $B$, respectively. Under certain additional assumptions, the couple $(C\cap D, C\cap D\cap L^{\infty}(μ))$ is $K$-closed in $(L^p(μ), L^{\infty}(μ))$. This statement covers, in particular, two cases analyzed previously: that of Hardy spaces on the two-dimensional torus and that of the coinvariant subspaces of the shift operator on the circle. Next, many situations when $A$ and $B$ are $w^*$-Dirichlet algebras also fit in this pattern.
math.FA↗