Bifurcations of Asymmetric Vortices in Symmetric Harmonic Traps

We show that, under the effect of rotation, symmetric vortices located at the center of a two-dimensional harmonic potential are subject to a pitchfork bifurcation with radial symmetry. This bifurcation leads to the family of asymmetric vortices, which precess constantly along an orbit enclosing the center of symmetry. The radius of the orbit depends monotonically on the difference between the rotation frequency and the eigenfrequency of negative Krein signature associated with the symmetric vortex. We show that both symmetric and asymmetric vortices are spectrally and orbitally stable with respect to small time-dependent perturbations for rotation frequencies exceeding the bifurcation eigenfrequency. At the same time, the symmetric vortex is a local minimizer of energy for supercritical rotation frequencies, whereas the asymmetric vortex corresponds to a saddle point of energy. For subcritical rotation frequencies, the symmetric vortex is a saddle point of the energy.