Platonic Solids and Symmetric Solutions of the N -vortex Problem on the Sphere

We consider the N -vortex problem on the sphere assuming that all vortices have equal strength. We develop a theoretical framework to analyse solutions of the equations of motion with prescribed symmetries. Our construction relies on the discrete reduction of the system by twisted subgroups of the full symmetry group that rotates and permutes the vortices. Our approach formalises and extends ideas outlined previously by Tokieda (C R Acad Sci, Paris I 333:943–946, 2001) and Soulière and Tokieda (J Fluid Mech 460:83–92, 2002) and allows us to prove the existence of several 1-parameter families of periodic orbits. These families either emanate from equilibria or converge to collisions possessing a specific symmetry. Our results are applied to show existence of families of small nonlinear oscillations emanating from the Platonic solid equilibria.