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A spectral characterization of the uniform continuity of strongly continuous groups
Authors:Khalid Latrach  J Martin Paoli  Pierre Simonnet
Institution:(1) Département de Mathématiques, Université Blaise Pascal (Clermont II), CNRS (UMR 6620) 24 avenue des Landais, 63170 Aubière, France;(2) Département de Mathématiques, Université de Corse, Quartier Grossetti, BP 52, F-20250 Corte, France
Abstract:Let X be a Banach space and $$(T(t))_{t \in {\mathbb{R}}}$$ a strongly continuous group of linear operators on X. Set $$\sigma^1(T(t))
 := \{ \frac{\lambda}{\mid \lambda \mid}\, : \,\lambda\, \in\, \sigma(T(t)) \}$$ and $$\chi(T) := \{t \in {\mathbb{R}} : \sigma^1(T(t)) \neq {\mathbb{T}}\}$$ where $${\mathbb{T}}$$ is the unit circle and $$\sigma(T(t))$$ denotes the spectrum of T(t). The main result of this paper is: $$(T(t))_{t \in {\mathbb{R}}}$$ is uniformly continuous if and only if $$\chi(T)$$ is non-meager. Similar characterizations in terms of the approximate point spectrum and essential spectra are also derived. Received: 14 June 2006, Revised: 27 September 2007
Keywords:Mathematics Subject Classification (2000)" target="_blank">Mathematics Subject Classification (2000)    47A10  47D03  54E52
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