Abstract
We study some problems of operator theory by using Berezin symbols approach. Namely, we investigate in terms of Berezin symbols invariant subspaces of isometric composition operators on \({\mathcal {H}}\left( \Omega \right) .\) We discuss operator corona problem, in particular, the Toeplitz corona problem. Further, we characterize unitary operators in terms of Berezin symbols. We show that the well known inequality \(w\left( A\right) \ge \frac{1}{2}\left\| A\right\| \) for numerical radius is not true for the Berezin number of operators, which is defined by \({\textrm{ber}}\left( A\right) :=\sup _{\lambda \in \Omega }\left| {\tilde{A}}\left( \lambda \right) \right| ,\) where \({\tilde{A}}\left( \lambda \right) :=\left\langle A\hat{k}_{\lambda },{\hat{k}}_{\lambda }\right\rangle \) is the Berezin symbol of operator \(A:{\mathcal {H}}\left( \Omega \right) \rightarrow {\mathcal {H}}\left( \Omega \right) .\) Finally, we provide a lower bound for \({\textrm{ber}}\left( A\right) .\)
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Acknowledgements
Dr. Pintu Bhunia would like to thank SERB, Govt. of India for the financial support in the form of National Post Doctoral Fellowship (N-PDF, File No. PDF/2022/000325) under the mentorship of Professor Apoorva Khare. Dr. M. Garayev would like to thank the Deanship of Scientific Research of King Saud University, the College of Science Research Center.
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Dr. Pintu Bhunia would like to thank SERB, Govt. of India for the financial support in the form of National Post Doctoral Fellowship (N-PDF, File No. PDF/2022/000325) under the mentorship of Professor Apoorva Khare
This article is part of the topical collection “Reproducing kernel spaces and applications” edited by Daniel Alpay
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Bhunia, P., Garayev, M.T., Paul, K. et al. Some New Applications of Berezin Symbols. Complex Anal. Oper. Theory 17, 96 (2023). https://doi.org/10.1007/s11785-023-01404-1
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DOI: https://doi.org/10.1007/s11785-023-01404-1
Keywords
- Reproducing kernel Hilbert space
- Berezin symbol
- Berezin number
- Invariant subspace
- Volterra integration operator
- Unitary operator