Spectral radius of S-essential spectra

  • C. Belabbaci University of Laghouat, Algeria
Keywords: S-essential spectra, measure of noncompactness, spectral radius, Fredholm operators

Abstract

In this paper, we study the spectral radius of some S-essential spectra of a bounded linear operator defined on a Banach space. More precisely, via the concept of measure of noncompactness,we show that for any two bounded linear operators $T$ and $S$ with $S$ non zero and non compact operator the spectral radius of the S-Gustafson, S-Weidmann, S-Kato and S-Wolf essential spectra are given by the following inequalities
\begin{equation}
\dfrac{\beta(T)}{\alpha(S)}\leq r_{e, S}(T)\leq \dfrac{\alpha(T)}{\beta(S)},
\end{equation}
where $\alpha(.)$ stands for the Kuratowski measure of noncompactness and $\beta(.)$ is defined in [11].
In the particular case when the index of the operator $S$ is equal to zero, we prove the last inequalities for the spectral radius of the S-Schechter essential spectrum. Also, we prove that the spectral radius of the S-Jeribi essential spectrum satisfies inequalities 2) when the Banach space $X$ has no reflexive infinite dimensional subspace and the index of the operator $S$ is equal to zero (the S-Jeribi essential spectrum, introduced in [7]
as a generalisation of the Jeribi essential spectrum).

Author Biography

C. Belabbaci, University of Laghouat, Algeria

Laboratory of Pure and Applied Mathematics Department of mathematics, University of Laghouat, Algeria

References

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Published
2020-10-06
How to Cite
1.
Belabbaci C. Spectral radius of S-essential spectra. Mat. Stud. [Internet]. 2020Oct.6 [cited 2020Oct.27];54(1):91-7. Available from: http://matstud.org.ua/ojs/index.php/matstud/article/view/22
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Articles