On unitarily equivalent submodules
R. DouglasJaydeb Sarkar
46E2246M2047A1347B32Hilbert modulesSilov moduleskernel Hilbert spacesinvariant subspacesisometries
The Hardy space on the unit ball in $\mathbb{C}^n$ provides examples of a quasi-free, finite rank Hilbert module which contains a pure submodule isometrically isomorphic to the module itself. For $n=1$ the submodule has finite codimension. In this note we show that this phenomenon can only occur for modules over domains in $\mathbb{C}$ and for finitely-connected domains only for Hardy-like spaces, the bundle shifts. Moreover, we show for essentially reductive modules that even when the codimension is infinite, the module is subnormal and again, on nice domains such as the unit ball, must be Hardy-like.
Indiana University Mathematics Journal
2008
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10.1512/iumj.2008.57.3406
10.1512/iumj.2008.57.3406
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Indiana Univ. Math. J. 57 (2008) 2729 - 2744
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