It is well-known that positivity of an operator semigroup has important consequences for its spectrum and thus for its asymptotic behaviour. However, it might come as a surprise that similar conclusions can still be made if we replace the positivity assumption by another geometric invariance condition, namely contractivity.
In this talk we present several theorems which show how contractivity of
an operator semigroup can affect its spectrum if the underlying Banach
space satisfies certain geometric conditions. As a consequence we obtain
the surprising result that a contractive, eventually norm-continuous