Comparison of spectra of absolutely regular distributions and applications

Abstract

We study the reduced Beurling spectra $sp_{{\cal A},V}(F)$ of functions $F \in L^1_{\rm loc} (\jj,X)$ relative to certain function spaces ${\cal A}\subset L^{\infty}(\jj,X)$ and $V\subset L^1 (\r)$ and compare them with other spectra including the weak Laplace spectrum. Here $\jj$ is $\r_+$ or $\r$ and $X$ is a Banach space. If $F$ belongs to the space $ \f^{\p}_{ar}(\r,X)$ of absolutely regular distributions and has uniformly continuous indefinite integral with $0\notin sp_{\A,\f(\r)} (F)$ (for example, if F is slowly oscillating and $\A$ is $\{0\}$ or $C_0 (\jj,X)$), then $F$ is ergodic. If $F\in \f^{\p}_{ar}(\r,X)$ and $M_h F (\cdot)= (1/h) \int_0^h F(\cdot+s)\,ds$ is bounded for all $h > 0$ (for example, if $F$ is ergodic) and if $sp_{C_0(\r,X),\f} (F)=\emptyset$, then ${F}*\psi \in C_0(\r,X)$ for all $\psi\in \f(\r)$. We show that Tauberian theorems for Laplace transforms follow from results about reduced spectra. Our results are more general than previous ones, and we demonstrate this through examples.