Dilation-commuting operators on power-weighted Orlicz classes

Abstract

Let $Φ_1$ and $Φ_2$ be nondecreasing functions from $\mathbb{R_+}=(0,\infty)$ onto itself. For $i=1,2$ and $γ\in \mathbb{R}$, define the Orlicz class $L_{Φ_{i}}(\mathbb{R_+})$ to be the set of Lebesgue-measurable functions $f$ on $\mathbb{R_+}$ such that \begin{equation*} \int_{\mathbb{R_+}} Φ_{i} \left( k|(Tf)(t)| \right) t^γdt < \infty \end{equation*} for some $k>0$. Our goal in this paper is to find conditions on $Φ_1$, $Φ_2$, $γ$ and an operator $T$ so that the assertions \begin{equation} T : L_{Φ_2,t^γ}(\mathbb{R_+}) \rightarrow L_{Φ_1,t^γ}(\mathbb{R_+}), \tag{I} \end{equation} and \begin{equation}\label{modularA} \int_{\mathbb{R_+}} Φ_1 \left( |(Tf)(t)| \right)t^γdt \leq K \int_{\mathbb{R_+}} Φ_2 \left( K|f(s)| \right)s^γds, \tag{M} \end{equation} in which $K>0$ is independent of $f$, say, simple on $\mathbb{R_+}$, are equivalent and to then find necessary and sufficient conditions in order that (\ref{modularA}) holds.