Schatten properties of commutators of fractional integrals on spaces of homogeneous type

Abstract

Extending classical results of Janson and Peetre (1988) on the Schatten class $S^p$ membership of commutators of Riesz potentials on the Euclidean space, we obtain analogous results for commutators $[b,T]$, where $T\in\{T_\varepsilon,\widetilde T_α\}$ belongs to either one of two natural classes of fractional integral operators on a space of homogeneous type. Our approach is based on recent related work of Hytönen and Korte on singular (instead of fractional) integrals; working directly with the kernels, it differs from the Fourier analytic considerations of Janson and Peetre, covering new operators even when specialised to $\mathbb R^d$. The cleanest case of our characterization in spaces of lower dimension $d> 2$ and satisfying a $(1,2)$-Poincaré inequality is as follows. For a parameter $\varepsilon \in (0,\frac{1}{2}-\frac{1}{d})$ describing the order of the fractional integral $T_\varepsilon $, we have a dichotomy: If $\frac{d}{1+d\varepsilon }<p<\frac{1}{\varepsilon}$, then $[b,T_{\varepsilon}]\in S^p$ if and only if $b$ belongs to a suitable Besov (or fractional Sobolev) space. If $0<p\leq \frac{d}{1+d\varepsilon }$, then $[b,T_{\varepsilon}]\in S^p$ if and only if $b$ is constant. This is analogous to the result for singular integrals, where a similar cut-off happens at $p=d$, formally corresponding to fractional order $\varepsilon =0$. We also obtain results for other parameter values, including dimensions $0<d\leq 2$. As an application, these results are used to show Schatten properties of commutators of fractional Bessel operators, complementing recent related results of Fan, Lacey, Li, and Xiong (2025) on commutators of singular integrals in the Bessel setting.