DIRECT CONSTRUCTION OF SYMMETRY-BREAKING DIRECTIONS IN BIFURCATION PROBLEMS WITH SPHERICAL SYMMETRY

We consider bifurcation problems in the presence of O(3) symmetry. Well known group-theoretic techniques enable the classification of all maximal isotropy subgroups of O(3), with associated mode numbers l is an element of N, leading to 1-dimensional fixed-point subspaces of the (2l+1)-dimensional space of spherical harmonics. In each case the so-called equivariant branching lemma can then be used to establish the existence of a local branch of bifurcating solutions having the symmetry of the respective subgroup. To first-order, such a branch is a precise linear combination of the 2l+ 1 spherical harmonics, which we call the bifurcation direction. Our work here is focused on the direct construction of these bifurcation directions, complementing the above-mentioned classification. The approach is an application of a general method for constructing families of symmetric spherical harmonics, based on differentiating the fundamental solution of Laplace's equation in R-3.