Explicit form of fundamental solutions to certain elliptic equations and associated $B$- and $C$-capacities

The main aim of this paper is to study the geometric and metric properties of $B$- and $C$-capacities related to problems of uniform approximation of functions by solutions of homogeneous second-order elliptic equations with constant complex coefficients on compact subsets of Euclidean spaces. In the harmonic case this problem is well known, and it was studied in detail in the framework of classical potential theory in the first half of the 20th century. For a wide class of equations mentioned above, we obtain two-sided estimates between the corresponding $B_{+}$- and $C_{+}$-capacities (defined in terms of potentials of positive measures) and the harmonic capacity in the same dimension. Our research method is based on new simple explicit formulae obtained for the fundamental solutions of the equations under consideration.