The continuum spectrum of nonrelativistic multi-frequency Proca stars

Multi-frequency Proca stars are excited equilibrium configurations of a selfgravitating massive vector field that coexist with conventional stationary states in the solution space of the $s=1$ Schr\"odinger-Poisson system. In this paper, we present a systematic study of the continuum spectrum of spherical multi-frequency Proca stars and show that they interpolate between the discrete set of stationary states of constant polarization. Furthermore, we also analyze their stability and demonstrate that a subset of these multi-frequency configurations are linearly stable against general perturbations. We briefly discuss the potential implications of multi-frequency states for proving the particle spin in ultralight dark matter models.