Ergodic Theory and Dynamical Systems

Research Article

Bifurcations of dynamic rays in complex polynomials of degree two

Pau Atelaa1

a1 Program in Applied Mathematics, University of Colorado, Boulder, CO 80309-526, USA

Abstract

In the study of bifurcations of the family of degree-two complex polynomials, attention has been given mainly to parameter values within the Mandelbrot set M (e.g., connectedness of the Julia set and period doubling). The reason for this is that outside M, the Julia set is at all times a hyperbolic Cantor set. In this paper weconsider precisely this, values of the parameter in the complement of M. We find bifurcations occurring not on the Julia set itself but on the dynamic rays landing on itfrom infinity. As the parameter crosses the external rays of M, in the dynamic plane the points of the Julia set gain and lose dynamic rays. We describe these bifurcations with the aid of a family of circle maps and we study in detail the case of the fixed points.

(Received June 06 1990)

(Revised February 11 1990)