This paper is concerned with α-times integrated C-semigroups for α > 0 and the associated abstract Cauchy problem: $u^{\text{'}}\left(t\right)=Au\left(t\right)+\frac{t^{\alpha -1}}{\Gamma \left(\alpha \right)}x$, t >0; u(0) = 0. We first investigate basic properties of an α-times integrated C-semigroup which may not be exponentially bounded. We then characterize the generator A of an exponentially bounded α-times integrated C-semigroup, either in terms of its Laplace transforms or in terms of existence of a unique solution of the above abstract Cauchy problem for every x in ${(\lambda -A)}^{-1}C\left(X\right)$.

Let $\left(T_t\right)$ be a C₀ semigroup with generator A on a Banach space X and let be an operator ideal, e.g. the class of compact, Hilbert-Schmidt or trace class operators. We show that the resolvent R(λ,A) of A belongs to if and only if the integrated semigroup $S_t:={\int }_0^t{T}_{s}ds$ belongs to . For analytic semigroups, $S_t\in$ implies $T_t\in$, and in this case we give precise estimates for the growth of the -norm of $T_t$ (e.g. the trace of $T_t$) in terms of the resolvent growth and the imbedding D(A) ↪ X.

We apply the contraction mapping theorem to establish some bounded and unbounded perturbation theorems concerning nondegenerate local α-times integrated semigroups. Some unbounded perturbation results of Wang et al. [Studia Math. 170 (2005)] are also generalized. We also establish some growth properties of perturbations of local α-times integrated semigroups.

A class of perturbing operators for locally Lipschitz continuous integrated semigroups is introduced according to the idea of Miyadera. The paper gives perturbation theorems of Miyadera type for such integrated semigroups.

We investigate the relations between local α-times integrated semigroups and (α + 1)-times integrated Cauchy problems, and then the relations between global α-times integrated semigroups and regularized semigroups.