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Essential numerical range and $C$-numerical range for unbounded operators

Essential numerical range and \(C\)-numerical range for unbounded operators
Authors: Hefti, Nicolas; Tretter, Christiane;

Essential numerical range and $C$-numerical range for unbounded operators

Abstract

Consider an unbounded operator \(T\) on a Hilbert space \(\mathcal{H}\). The authors introduce a new type of essential numerical range for \(T\), called \(W_{e5}(T)\) (essential numerical range of type 5). They show, for instance, that \(W_{e5}(T)\) is closed, convex, and contains the essential spectrum \(\sigma_e(T)\). It is also proved that \(W_{e5}(T)\subseteq W_e(T)\), where \(W_e(T)\) denotes the usual essential numerical range of \(T\), and that the inclusion may be strict. Moreover, the authors introduce a notion of \(C\)-numerical range \(W_C(T)\), where \(T\) is assumed to be densely defined and closed and \(C\) is a compact operator on \(\mathcal{H}\). A relation between \(W_{e5}(T)\) and \(W_C(T)\) for finite-rank operators \(C\) is established.

Related Organizations
Keywords

essential spectrum, Numerical range, numerical radius, \(C\)-numerical range, essential numerical range, Spectrum, resolvent

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
1
Average
Average
Average