Torus-breakdown near a Bykov attractor: a case study

There are few explicit examples in the literature of vector fields exhibiting complex dynamics that may be proved analytically. This paper reports numerical experiments performed for an explicit two-parameter family of vector fields unfolding an attracting heteroclinic network, linking two saddle-foci with $(\mathbb{SO}(2) \oplus \mathbb{Z}_2)$-symmetry. The vector field is the restriction to $\mathbb{S}^3$ of a polynomial vector field in $\mathbb{R}^4$. We investigate global bifurcations due to symmetry-breaking and we detect strange attractors via a phenomenon called Torus-Breakdown theory. We explain how an attracting torus gets destroyed by following the changes in the invariant manifolds of the saddle-foci. Although a complete understanding of the corresponding bifurcation diagram and the mechanisms underlying the dynamical changes is still out of reach, using a combination of theoretical tools and computer simulations, we have uncovered some complex patterns for the symmetric family under analysis. This also suggests a route to obtain rotational horseshoes; additionally, we give an attempt to elucidate some of the bifurcations involved in an Arnold wedge.