Soient $a_1,...,a_n$ des éléments d’une $b$-algèbre commutative unifère $A$. On définit et étudie un “spectre” de $a=(a_1,...,a_n)$ qui dépend de la croissance des fonctions $u_1\left(s\right),...,u_n\left(s\right)$ de l’égalité spectrale$$(a_1-s_1)u_1\left(s\right)+\cdots +(a_n-s_n)u_n\left(s\right)=1$$près du spectre simultané. À partir des propriétés de ce spectre, on construit un calcul fonctionnel qui, réduit au cas banachique, s’étend à certaines fonctions supposées seulement holomorphes à l’intérieur du spectre simultané. Ce calcul fonctionnel permet aussi d’étudier la régularité des éléments $a_1,...,a_n$ et des fonctions $u_1\left(s\right),...,u_n\left(s\right)$.

We study a class of closed linear operators on a Banach space whose nonzero spectrum lies in the open left half plane, and for which $0$ is at most a simple pole of the operator resolvent. Our spectral theory based methods enable us to give a simple proof of the characterization of $C_0$-semigroups of bounded linear operators with asynchronous exponential growth, and recover results of Thieme, Webb and van Neerven. The results are applied to the study of the asymptotic behavior of the solutions to a singularly...

The relationship between the joint spectrum γ(A) of an n-tuple $A=(A_1,...,A_n)$ of selfadjoint operators and the support of the corresponding Weyl calculus T(A) : f ↦ f(A) is discussed. It is shown that one always has γ(A) ⊂ supp (T(A)). Moreover, when the operators are compact, equality occurs if and only if the operators $A_j$ mutually commute. In the non-commuting case the equality fails badly: While γ(A) is countable, supp(T(A)) has to be an uncountable set. An example is given showing that, for non-compact operators,...

We study the continuity of the generalized Drazin inverse for elements of Banach algebras and bounded linear operators on Banach spaces. This work extends the results obtained by the second author on the conventional Drazin inverse.