Strict positive definiteness on spheres via disk polynomials

Abstract

We characterize complex strictly positive definite functions on spheres in two cases, the unit sphere of ℂq, q≥3, and the unit sphere of the complex ℓ2. The results depend upon the Fourier-like expansion of the functions in terms of disk polynomials and, among other things, they enlarge the classes of strictly positive definite functions on real spheres studied in many recent papers.