Muckenhoupt-weighted $L_q(L_p)$ boundedness for time-space fractional nonlocal operators

Abstract: Based on the $\phi(\Delta)$-type operator studied by Kim \cite[\emph{Adv.~Math.}]{Kim2}, where $\phi$ is a Bernstein function, we establish weighted $L_{q}(L_{p})$ estimates for solutions to the following fractional evolution equation: $$ \partial_{t}^{\alpha}w(t,x) = \phi(\Delta)w(t,x) + h(t,x), \quad t > 0, \; x \in \mathbb{R}^{d}, $$ where $\partial_{t}^{\alpha}$ denotes the Caputo derivative of $0 < \alpha < 1$. To be specific, for all $1 < p, q < \infty$, we demonstrate that $$ \int_{0}^{\infty} \left( \int_{\mathbb{R}^{d}} \left| \phi(\Delta)w \right|^{p} \mu_{1}(x) \, dx \right)^{\frac{q}{p}} \mu_{2}(t) \, dt \leq C \int_{0}^{\infty} \left( \int_{\mathbb{R}^{d}} |h|^{p} \mu_{1}(x) \, dx \right)^{\frac{q}{p}} \mu_{2}(t) \, dt, $$ where $\mu_{1}(x) \in A_{p}(\mathbb{R}^{d})$ and $\mu_{2}(t) \in A_{q}(\mathbb{R})$ are \emph{Muckenhoupt} weights.~Our proof relies on harmonic analysis techniques, using fundamental tools including the \emph{Fefferman-Stein} inequality and \emph{Hardy-Littlewood} maximal estimates in weighted $L_q(L_p)$ spaces, and \emph{sharp function} estimates for solution operators. In particular, our results extend the work of Han and Kim (2020, J. Differ. Equ.,269:3515-3550) and complement the work of Dong (2023, Calc. Var. Partial Differ. Equ., 62:96).