arXiv subjects
Publications and source records attributed to Tomás Merchán.
We study the limiting behavior of $r$-maximum distance minimizers and the asymptotics of their $1$-dimensional Hausdorff measures as $r$ tends to zero in several contexts, including situations involving objects of fractal nature.
For a set $E$ of positive and finite length, we prove that if the Huovinen transform (the convolution operator with kernel $z^k/|z|^{k+1}$ for an odd number $k$) associated to $E$ exists in principal value, then $E$ is rectifiable.
Fix $d\geq 2$ and $s\in (0,d)$. In this paper we introduce a notion called small local action associated to a singular integral operator, which is a necessary condition for the existence of principal value integral to exist. Our goal is to understand the geometric properties of a measure for which an associated singular integral has small local action. We revisit Mattila's theory of symmetric measures and relate, under the condition that the measure has finite upper density, the existence of small local action to the cost of transporting the measure to a collection of symmetric measures. As applications, we obtain a soft proof of a theorem of Tolsa and Ruiz-de-Villa on the non-existence of a measure with positive and finite upper density for which the principal value integral associated with the $s$-Riesz transform exists if $s\not\in \mathbb{Z}$. Furthermore, we provide a considerable generalization of this theorem if $s\in (d-1,d)$.
In this paper we study the relationship between two fundamental regularity properties of an $s$-dimensional Calderón-Zygmund operator (CZO) acting on a Borel measure $μ$ in $\mathbb{R}^d$, with $s\in (0,d)$. In the classical case when $s=d$ and $μ$ is equal to the Lebesgue measure, Calderón and Zygmund showed that if a CZO is bounded in $L^2$ then the principal value integral exists almost everywhere. However, there are by now several examples showing that this implication may fail for lower-dimensional kernels and measures, even when the CZO has a homogeneous kernel consisting of spherical harmonics. We introduce sharp geometric conditions on $μ$, in terms of certain scaled transportation distances, which ensure that an extension of the Calderón-Zygmund theorem holds. These conditions are necessary and sufficient in the cases of the Riesz transform and the Huovinen transform. Our techniques build upon prior work by Mattila and Verdera, and incorporate the machinery of symmetric measures, introduced to the area by Mattila.