2180 articles – 2572 references  [version française]
 HAL: hal-00672703, version 1
 arXiv: 1202.3962
 A sharpened Schwarz-Pick operatorial inequality for nilpotent operators
 (2012-02-17)
 Let denote by $S(\phi)$ the extremal operator defined by the compression of the unilateral shift $S$ to the model subspace $H(\phi)=H^{2} \ominus \phi H^{2}$ as the following $S(\phi)f(z)=P(zf(z)),$ where $P$ denotes the orthogonal projection from the Hardy space $H^{2}$ onto $H(\phi)$ and $\phi$ is an inner function on the unit disc. In this mathematical notes, we give an explicit formula of the numerical radius of the truncated shift $S(\phi)$ in the particular case where $\phi$ is a finite Blaschke product with unique zero and an estimate on the general case. We establish also a sharpened Schwarz-Pick operatorial inequality generalizing a U. Haagerup and P. de la Harpe result for nilpotent operators
 1: Institut Camille Jordan (ICJ) CNRS : UMR5208 – Université Claude Bernard - Lyon I – Ecole Centrale de Lyon – Institut National des Sciences Appliquées (INSA) - Lyon
 Subject : Mathematics/Functional Analysis