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Similarity to a contraction and hypercontractivity of composition operators
Authors:Nizar Jaoua
Institution:Department of Mathematics, Université Lille I, Cité Scientifique, F-59655 Villeneuve d'Ascq, France
Abstract:On the Hardy spaces $H^p$ with $1 \leq p<\infty$, we consider the composition operators induced by analytic self-maps of the open unit disc $D$. First, we characterize those which are similar to contractions. Then, we give some necessary and sufficient conditions for them to be hypercontractive. Finally, we prove that, among those ones, only the zero-symbol composition operator sends $H^p$ into $H^{\infty}$ with a norm less than or equal to $1$.

Keywords:Composition operators  Hardy spaces  contraction  hypercontractive (or $\beta$-contractive) operator
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