Measures that define a compact cauchy transform

© 2019 American Mathematical Society. The aim of this work is to provide a geometric characterization of the positive Radon measures µ with compact support on the plane such that the associated Cauchy transform defines a compact operator from L 2 (µ) to L 2 (µ). It turns out that a crucial role is played by the density of the measure and by its Menger curvature.