ABOUT THE UNFOLDING OF A HOPF-ZERO SINGULARITY

Abstract

We study arbitrary generic unfoldings of a Hopf-zero singularity of codimension two. They can be written in the following normal form: {x' = -y + mu x - axz + A(x,y,z,lambda,mu) y' = x + mu y - ayz + B(x,y,z,lambda,mu) z' = z(2) vertical bar lambda vertical bar b(x(2) vertical bar y(2)) vertical bar C(x,y,z,lambda,mu), with a > 0, b > 0 and where A, B, C are C-infinity or C-omega functions of order O(vertical bar vertical bar(x,y,z,lambda,mu)vertical bar vertical bar(3)). Despite that the existence of Shilnikov homoclinic orbits in unfoldings of Hopf-zero singularities has been discussed previously in the literature, no result valid for arbitrary generic unfoldings is available. In this paper we present new techniques to study global bifurcations from Hopf-zero singularities. They allow us to obtain a general criterion for the existence of Shilnikov homoclinic bifurcations and also provide a detailed description of the bifurcation set. Criteria for the existence of Bykov cycles are also provided. Main tools are a blow-up method, including a related invariant theory, and a novel approach to the splitting functions of the invariant manifolds. Theoretical results are applied to the Michelson system and also to the so called extended Michelson system. Paper includes thorough numerical explorations of dynamics for both systems.