On Pointwise ℓ<sup>r</sup> -Sparse Domination in a Space of Homogeneous Type
Emiel Lorist
Abstract
<p>We prove a general sparse domination theorem in a space of homogeneous type, in which a vector-valued operator is controlled pointwise by a positive, local expression called a sparse operator. We use the structure of the operator to get sparse domination in which the usual ℓ<sup>1</sup>-sum in the sparse operator is replaced by an ℓ<sup>r</sup>-sum. This sparse domination theorem is applicable to various operators from both harmonic analysis and (S)PDE. Using our main theorem, we prove the A<sub>2</sub>-theorem for vector-valued Calderón–Zygmund operators in a space of homogeneous type, from which we deduce an anisotropic, mixed-norm Mihlin multiplier theorem. Furthermore, we show quantitative weighted norm inequalities for the Rademacher maximal operator, for which Banach space geometry plays a major role.</p>