In [1] D. Harrington and R. Whitley examined several questions of seminormality for composition operators. In that article they raise the question of finding a measure theoretic characterization of hyponormality for composition operators. In this article we establish criteria for hyponormality for weighted composition operators. By restricting attention to the case of weight function equal to 1...

The norm of a bounded composition operator induced by a disc automorphism is estimated on weighted Hardy spaces H(β) in which the classical Hardy space is continuously embedded. The estimate obtained is accurate in the sense that it provides the exact norm for particular instances of the sequence β. As a by-product of our results, an estimate for the norm of any bounded composition operator on ...

Let E be a Banach space, with unit ball BE . We study the spectrum and the essential spectrum of a composition operator on H∞(BE) determined by an analytic symbol with a fixed point in BE . We relate the spectrum of the composition operator to that of the derivative of the symbol at the fixed point. We extend a theorem of Zheng to the context of analytic symbols on the open unit ball of a Hilbe...

We investigate the connection between the geometry of the image domain of an analytic function mapping the unit disk into itself and the membership of the composition operator induced by this function in the Schatten classes. The purpose is to provide solutions to Lotto’s conjectures and show a new compact composition operator which is not in any of the Schatten classes. 2000 Mathematics Subjec...

We give examples of composition operators CΦ on H(D) showing that the condition ‖Φ‖∞ = 1 is not sufficient for their approximation numbers an(CΦ) to satisfy limn→∞[an(CΦ)] √ n = 1, contrary to the 1-dimensional case. We also give a situation where this implication holds. We make a link with the Monge-Ampère capacity of the image of Φ. Key-words : approximation numbers; Bergman space; bidisk; co...

The standard operational semantics of the sequential composition operator gives rise to unbounded branching and forgetfulness when transparent process expressions are put in sequence. Due to transparency, the correspondence between context-free and pushdown processes fails modulo bisimilarity, and it is not clear how to specify an always terminating half counter. We propose a revised operationa...

The standard operational semantics of the sequential composition operator gives rise to unbounded branching and forgetfulness when transparent process expressions are put in sequence. Due to transparency, the correspondence between context-free and push-down processes fails modulo bisimilarity, and it is not clear how to specify an always terminating half counter. We propose a revised operation...

Let φ(z) = (φ1(z), · · · , φn(z)) be a holomorphic self-map of Bn and ψ(z) a holomorphic function on Bn, and H(Bn) the class of all holomorphic functions on Bn, where Bn is the unit ball of C , the weight composition operator Wψ,φ is defined by Wψ,φ = ψf(φ) for f ∈ H(Bn). In this paper we estimate the essential norm for the weighted composition operator Wψ,φ acting from the Hardy space H to H (...

We study the decay of approximation numbers of compact composition operators on the Dirichlet space. We give upper and lower bounds for these numbers. In particular, we improve on a result of O. El-Fallah, K. Kellay, M. Shabankhah and A. Youssfi, on the set of contact points with the unit circle of a compact symbolic composition operator acting on the Dirichlet space D. We extend their results ...