Singular operators with antisymmetric kernels, related capacities, and Wolff potentials

We consider a generalization of the Riesz operator in $R^d$ and obtain estimates for its norm and for related capacities via the modified Wolff potential. These estimates are based on the certain version of $T1$ theorem for Calder\'on-Zygmund operators in metric spaces. We extend two versions of Calder\'on-Zygmund capacities in $R^d$ to metric spaces and establish their equivalence (under certain conditions). As an application, we extend the known relations between $s$-Riesz capacities, $0<s<d$, and the capacities in Nonlinear Potential Theory, to the case $s=0$.