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arXiv · 2110.06540

Adjoint Pairs and Unbounded Normal Operators

Konrad Schmüdgen
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Abstract

An adjoint pair is a pair of densely defined linear operators $A, B$ on a Hilbert space such that $\langle Ax,y\rangle=\langle x,By\rangle$ for $x\in \cD(A), y \in \cD(B).$ We consider adjoint pairs for which $0$ is a regular point for both operators and associate a boundary triplet to such an adjoint pair. Proper extensions of the operator $B$ are in one-to-one correspondence $T_\cC\leftrightarrow \cC $ to closed subspaces $\cC$ of $\cN(A^*)\oplus\cN(B^*)$. In the case when $B$ is formally normal and $\cD(A)=\cD(B)$, the normal operators $T_\cC$ are characterized. Next we assume that $B$ has an extension to a normal operator with bounded inverse. Then the normal operators $T_\cC$ are described and the case when $\cN(A^*)$ has dimension one is treated.

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Konrad Schmüdgen. 2021-10-13. Adjoint Pairs and Unbounded Normal Operators. https://arxiv.org/abs/2110.06540

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