Seminário Análise Funcional e Aplicações 

23/05/2008, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática
Chafiq Benhida, Université de Lille 1, France

Multicontractions, Poisson kernel and characteristic function

The theory of row contractions (called also multicontractions) as initiated by Gelu Popescu is the most notable achievement in the aim of extending the well known Sz.-Nagy-Foias dilation theory of contractions on a Hilbert space. Two objects related to a multicontraction play a significant role in this theory: the Poisson kernel and the characteristic function. The Poisson kernel is an important tool used by Popescu in order to prove the von Neumann inequality for row contractions; the characteristic function is essential in the model theory of completely noncoisometric multicontractions. We give the behaviour of this two objects with respect to the action of the group of unitarily implemented automorphisms of the algebra generated by creation operators on the Fock space.