Asymmetric Fuglede-Putnam Theorem for Unbounded M-Hyponormal Operators

TL;DR

This paper extends the Fuglede-Putnam theorem to unbounded M-hyponormal operators, establishing operator relations and reducing subspaces under certain bounded and unbounded operator conditions.

Contribution

It proves an asymmetric Fuglede-Putnam theorem for unbounded M-hyponormal operators, a significant generalization of classical results.

Findings

Operator $AB^* \\subseteq TA$ implies $AB \\subseteq T^*A$.

Reduces $B$ to a normal operator on a subspace.

Reduces $T$ to a normal operator on a subspace.

Abstract

A closed densely defined operator $ T $ on a Hilbert space $ \mathcal{H} $ is callled $M$-hyponormal if $\mathcal{D}(T) \subset \mathcal{D}(T^{*}) $ and there exists $ M > 0 $ for which $ \parallel(T-zI)^{*}x \parallel \leq M \parallel(T-zI)x \parallel $ for all $ z \in \mathbb{C}$ and for all $ x\in \mathcal{D}(T)$. In this paper, we prove that if bounded linear operator $ A : \mathcal{H} \rightarrow \mathcal{K}$ is such that $ AB^*\subseteq TA $, where $ B $ is a closed subnormal (resp. a closed $ M $-hyponormal) on $\mathcal{H}$, $ T $ is a closed $ M $-hyponormal (resp. a closed subnormal) on $\mathcal{H}$, then (i) $ AB\subseteq T^*A, $ (ii) $ {\overline{ran(A^{*})}} $ reduces $ B $ to the normal operator $ B\vert_{{\overline{ran(A^{*})}}}, $ and (iii) $ {\overline{ran(A)}} $ reduces $ T $ to the normal operator $ T\vert_{{\overline{ran(A)}}}.$