Soit $X$ un espace riemannien symétrique et $C_0\left(X\right)$ l’espace des fonctions continues sur $X$ tendant vers 0 à l’infini. On démontre qu’un opérateur $(D_{A^{\text{'}}},A)$, invariant par les isométries de $X$, engendre un semi-groupe fortement continu de contractions sur $C_0\left(X\right)$ s’il est dissipatif et si son domaine contient les fonctions de classe ${𝒞}^{\infty }$ à support compact.

Let $D$ be domain in a complex Banach space $X$, and let $\rho$ be a pseudometric assigned to $D$ by a Schwarz-Pick system. In the first section of the paper we establish several criteria for a mapping $f:D\to X$ to be a generator of a $\rho$-nonexpansive semigroup on $D$ in terms of its nonlinear resolvent. In the second section we let $X=H$ be a complex Hilbert space, $D=B$ the open unit ball of $H$, and $\rho$ the hyperbolic metric on $B$. We introduce the notion of a $\rho$-monotone mapping and obtain simple characterizations of generators...

The aim of the paper is two-fold. First, we investigate the ψ-Bessel potential spaces on ${ℝ}_{0+}^{n+1}$ and study some of their properties. Secondly, we consider the fractional powers of an operator of the form $-A_{\pm }=-\psi \left(D_{x^{\text{'}}}\right)\pm \partial /\left(\partial x_{n+1}\right)$, $(x^{\text{'}},x_{n+1})\in {ℝ}_{0+}^{n+1}$, where $\psi \left(D_{x^{\text{'}}}\right)$ is an operator with real continuous negative definite symbol ψ: ℝⁿ → ℝ. We define the domain of the operator $-{(-A_{\pm })}^{\alpha }$ and prove that with this domain it generates an $L_p$-sub-Markovian semigroup.

Let be a locally compact Hausdorff space. Let $A_i$, i = 0,1,...,N, be generators of Feller semigroups in C₀() with related Feller processes $X_i=X_i\left(t\right),t\ge 0$ and let ${\alpha }_i$, i = 0,...,N, be non-negative continuous functions on with ${\sum }_{i=0}^N{\alpha }_i=1$. Assume that the closure A of ${\sum }_{k=0}^N{\alpha }_k{A}_k$ defined on ${\bigcap }_{i=0}^N\left(A_i\right)$ generates a Feller semigroup T(t), t ≥ 0 in C₀(). A natural interpretation of a related Feller process X = X(t), t ≥ 0 is that it evolves according to the following heuristic rules: conditional on being at a point p ∈ , with probability ${\alpha }_i\left(p\right)$, the process...