Date & Time: Tuesday, November 8, 2011, 15:00-16:00
Venue: Ramanujan Hall

Title: n-contractivity and k-hyponormality

Speaker: Prof. George Exner, Bucknell University, USA

Abstract: The subnormality of a Hilbert space operator has two standard characterizations, one due to Bram-Halmos and the other to Agler-Embry. These characterizations naturally give rise to the classes of k-hyponormal (k=1, 2, ...) and n-contractive (n=1, 2, ...) operators respectively.

While relationships between the two collections of classes are not well understood, we consider some of the history of results in this area and exhibit some families of perturbations of subnormal weighted shift operators (such as perturbations of the Bergman shift) for which the relationship is unexpectedly strong.