Gravitating vortices and symplectic reduction by stages

Abstract

We undertake a novel approach to the existence problem for gravitating vortices on a Riemann surface based on symplectic reduction by stages, which seems to be new in the PDE as well as the field theory literature. The main technical tool for our study is the reduced $\alpha$-K-energy, for which we establish convexity properties by means of finite-energy pluripotential theory, as recently applied to the study of constant scalar curvature Kähler metrics. Using these methods, we prove that the existence of solutions to the gravitating vortex equations on the sphere implies the polystability of the effective divisor defined by the zeroes of the Higgs field. This approach also enables us to establish the uniqueness of gravitating vortices in any admissible Kähler class, in the absence of automorphisms. Lastly, we prove the existence of solutions for the gravitating vortex equations for genus $g\ge 1$ and certain ranges of the coupling constant $\alpha$ and the volume.