Spectral inclusions and stability results for strongly continuous semigroups.
In this paper we characterize the class of polynomially Riesz strongly continuous semigroups on a Banach space . Our main results assert, in particular, that the generators of such semigroups are either polynomially Riesz (then bounded) or there exist two closed infinite dimensional invariant subspaces and of with such that the part of the generator in is unbounded with resolvent of Riesz type while its part in is a polynomially Riesz operator.
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