An extrapolation theorem for the $H^\infty$calculus on $L^p(\Omega;X)$

Abstract

Let $(A_p)_{1 < p < \infty}$ be a consistent family of sectorial operators on $L^p(\Omega; X)$, where $\Omega$ is a homogeneous space with doubling property and $X$ is a Banach space having the Radon-Nykodým property. If $A_{p_0}$ has a bounded {$H^\infty$ calculus}{} for some $1 < p_0 < \infty$ and the resolvent or the semigroup generated by $A_{p_0}$ fulfills a Poisson estimate, then it is proved that $A_p$ has a bounded {$H^\infty$ calculus}{} for all $1 < p \le p_0$ and even for $1 < p < \infty$ if $X$ is reflexive. In order to do so, the Calderón-Zygmund decomposition is generalized to the vector-valued setting.