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 $u_1\left(s\right),...,u_n\left(s\right)$.

It is known that $ℬ\left({\ell }^p\right)$ is not amenable for p = 1,2,∞, but whether or not $ℬ\left({\ell }^p\right)$ is amenable for p ∈ (1,∞) ∖ 2 is an open problem. We show that, if $ℬ\left({\ell }^p\right)$ is amenable for p ∈ (1,∞), then so are ${\ell }^{\infty }\left(ℬ\left({\ell }^p\right)\right)$ and ${\ell }^{\infty }\left(\left({\ell }^p\right)\right)$. Moreover, if ${\ell }^{\infty }\left(\left({\ell }^p\right)\right)$ is amenable so is ${\ell }^{\infty }(,\left(E\right))$ for any index set and for any infinite-dimensional ${ℒ}^p$-space E; in particular, if ${\ell }^{\infty }\left(\left({\ell }^p\right)\right)$ is amenable for p ∈ (1,∞), then so is ${\ell }^{\infty }\left(\left({\ell }^p\oplus \ell ²\right)\right)$. We show that ${\ell }^{\infty }\left(\left({\ell }^p\oplus \ell ²\right)\right)$ is not amenable for p = 1,∞, but also that our methods fail us if p ∈ (1,∞). Finally, for p ∈ (1,2) and a free ultrafilter over ℕ, we exhibit...

Dans cet article, suivant une idée de W. Żelazko dans [8], on donne plusieurs caractérisations des algèbres localement m-convexes ayant tous leurs éléments à spectre borné. Cela nous permet d'obtenir la caractérisation, parmi les algèbres localement m-convexes, de celles qui ont l'espace des caractères équiborné. On obtient, comme conséquence immédiate de cette caractérisation, que dans une algèbre localement m-convexe complète, commutative et unitaire dont tous les éléments sont à spectre borné,...

We show that the Banach algebras with continuous involution are the Banach algebras which admit a harmonic functional calculus, while we prove that the hermitian commutative Banach algebras are exactly the involutive commutative Banach algebras that admit a real analytic functional calculus.

We prove that C*-algebras for an equivalent norm are the involutive Banach algebras which admit the continuous functional calculus.

En el presente artículo se expone de modo resumido una caracterización de los anillos de funciones diferenciables de una variedad.

Let G be the set of invertible elements of a normed algebra A with an identity. For some but not all subsets H of G we have the following dichotomy. For x ∈ A either $cx{c}^{-1}=x$ for all c ∈ H or $sup\parallel cx{c}^{-1}\parallel :c\in H=\infty$. In that case the set of x ∈ A for which the sup is finite is the centralizer of H.

We study the notion of character Connes amenability of dual Banach algebras and show that if $A$ is an Arens regular Banach algebra, then $A^{**}$ is character Connes amenable if and only if $A$ is character amenable, which will resolve positively Runde’s problem for this concept of amenability. We then characterize character Connes amenability of various dual Banach algebras related to locally compact groups. We also investigate character Connes amenability of Lau product and module extension of Banach algebras....

Let 𝓐 be a Banach algebra and let ϕ be a nonzero character on 𝓐. We give some necessary and sufficient conditions for the left ϕ-contractibility of 𝓐 as well as several hereditary properties. We also study relations between homological properties of some Banach left 𝓐-modules, the left ϕ-contractibility and the right ϕ-amenability of 𝓐. Finally, we characterize the left character contractibility of various Banach algebras related to locally compact groups.

Character inner amenability for a certain class of Banach algebras including projective tensor products, Lau products and module extensions is investigated. Some illuminating examples are given.

Let 𝓐 be a Banach algebra and let ϕ be a nonzero character on 𝓐. We introduce and study a new notion of amenability for 𝓐 based on existence of a ϕ-approximate diagonal by modifying the concepts of ϕ-amenability and pseudo-amenability. We then apply these results to characterize ϕ-pseudo-amenability of various Banach algebras related to locally compact groups such as group algebras, measure algebras, certain dual algebras and Lebesgue-Fourier algebras.