Tongues in degree 4 Blaschke products

Abstract

The goal of this paper is to investigate the family of Blasche products B_a , which is a rational family of perturbations of the doubling map. We focus on the tongue-like sets which appear in its parameter plane. We first study their basic topological properties and afterwards we investigate how bifurcations take place in a neighborhood of their tips. Finally we see how the fixed tongue extends beyond its natural domain of definition.