Deformations of Reproducing Kernel Hilbert Spaces on Homogeneous Subvarieties of the Unit Ball

We study the relationships between a subvariety of the open unit ball in the complex $d$-dimensional space ${\mathbb{C}}^d$, the reproducing kernel Hilbert space (RKHS) obtained by restricting the Drury-Arveson space to the variety, and its multiplier algebra. We show that if two such RKHSs are almost isometrically isomorphic as RKHSs, their multiplier algebras are likewise almost completely isometrically isomorphic as multiplier algebras. In such cases, the underlying varieties are almost automorphically equivalent. For tractable homogeneous varieties, we further show that if the corresponding multiplier algebras are almost completely isometrically isomorphic as multiplier algebras or one variety is almost the image of the other under a unitary transformation, then the associated RKHSs are almost isometrically isomorphic as RKHSs.