Vector-Valued Sub-Bergman Spaces: Range Inclusions and Nonrigidity
Let $\mathcal E$ be a separable Hilbert space, $B\in H^\infty_1(L(\mathcal E))$, and $α>-1$. Associated with the Toeplitz operator $T_B$ on the vector-valued weighted Bergman space $A^2_{α,\mathcal E}$ are the sub-Bergman spaces $\mathcal A_α(B)$ and $\mathcal A_α(B^*)$. In this paper, we prove that \[ \mathcal A_α(B)\supset A^2_{α-1,\mathcal H(B(0))} \quad\text{and}\quad \mathcal A_α(B^*)\supset A^2_{α-1,\mathcal H(B(0)^*)}. \] This confirms a conjecture of \cite{GLM26}. We also construct an infinite-dimensional two-sided inner function $B$ such that $\|B(0)\|<1$ and \[ \mathcal A_α(B)\approx \mathcal A_α(B^*)\approx A^2_{α-1,\mathcal E}, \] but $B$ is not a finite Blaschke-Potapov product. This example shows that the finite-dimensional rigidity theorem of \cite{GLM26} does not extend to infinite-dimensional coefficient spaces.