Tuesday, March 18, 2025, 2:15 to 3:00 PM in M305
Fanglei Wu, University of Eastern Finland
Composition semigroups on spaces of analytic functions in the unit disc
In this talk, I am going to show some popular research topics related to composition semigroups, which mainly include the following problems: 1. When are composition semigroups strongly continuous? 2. If composition semigroups are strongly continuous, then what properties do they have? How to depict the spectra of their infinitesimal generators? 3. How to use composition semigroups to deal with other problems? I will also present some unsolved questions.
Thursday, March 6, 2025, 4:15 PM
Finnish Mathematical Society Colloquium
Haakan Hedenmalm, KTH, Sweden
Conformally invariant Gaussian analytic functions, holomorphic correlations, and operator symbols of contractions
Monday, February 17, 2025, 3:15 to 4:00 PM in M304
Hicham Arroussi, University of Helsinki, Finland
Embedding theorems and generalized weighted composition operators on large Bergman spaces
We characterize boundedness, compactness and Schatten class membership of the generalized weighted composition operator between exponentially weighted Bergman spaces. We also obtain estimates for the norm of the derivatives of the corresponding reproducing kernel and describe bounded and compact differentiation operators, which generalize the embedding theorems of Luecking and the criteria for bounded and compact Carleson measures. Joint work with J. Taskinen and J. Virtanen.
Friday, February 7, 2025, 2:15 to 3:00 PM in M106
Santeri Miihkinen, University of Reading, UK
Toeplitz operators with piecewise continuous symbols on Hardy spaces
We consider Toeplitz operators acting on the Hardy spaces Hp for 1 ≤ p < ∞. Geometric descriptions of the essential spectra of Toeplitz operators up to piecewise continuous symbols are well known for 1 < p < ∞. We will investigate what happens in the case p = 1. The talk is based on joint work with J. Virtanen.
Friday, January 24, 2025, 2:15 to 3:00 PM in M107
David Norrbo, University of Reading, UK
Norm, essential norm and maximal sequences on certain classes of Banach spaces
Let X be a separable reflexive space with two additional properties, the compact approximation property and (m_p). This class of spaces is a generalization of l^p spaces. Two interesting questions are: for which operators are the norm and the essential norm equal? And which operators are norm-attaining? It turns out that these questions can be answered based on the minimal and maximal weak cluster points of the operators’ maximizing sequences. As a consequence, a non-standard formula for the essential norm is obtained.
