On the boundedness of generalized Cesàro operators on Sobolev spaces (1304.1622v1)

Abstract: For $\beta>0$ and $p\ge 1$, the generalized Ces`aro operator $$ \mathcal{C}\beta f(t):=\frac{\beta}{t^\beta}\int_0^t (t-s)^{\beta-1}f(s)ds $$ and its companion operator $\mathcal{C}\beta^*$ defined on Sobolev spaces $\mathcal{T}p^{(\alpha)}(t^\alpha)$ and $\mathcal{T}_p^{(\alpha)}(| t|^\alpha)$ (where $\alpha\ge 0$ is the fractional order of derivation and are embedded in $L^p(\RR^+)$ and $L^p(\RR)$ respectively) are studied. We prove that if $p>1$, then $\mathcal{C}\beta$ and $\mathcal{C}\beta^*$ are bounded operators and commute on $\mathcal{T}_p^{(\alpha)}(t^\alpha)$ and $\mathcal{T}_p^{(\alpha)}(| t|^\alpha)$. We show explicitly the spectra $\sigma (\mathcal{C}\beta)$ and $\sigma (\mathcal{C}\beta^*)$ and its operator norms (which depend on $p$). For $1< p\le 2$, we prove that $ \hat{{\mathcal C}\beta(f)}={\mathcal C}\beta^*(\hat{f})$ and $\hat{{\mathcal C}\beta^*(f)}={\mathcal C}_\beta(\hat{f})$ where $\hat{f}$ is the Fourier transform of a function $f\in L^p(\RR)$.