$\ell$-Boson stars

Abstract

We present new, fully nonlinear numerical solutions to the static, spherically symmetric Einstein-Klein-Gordon system for a collection of an arbitrary odd number $N$ of complex scalar fields with an internal $U(N)$ symmetry and no self-interactions. These solutions, which we dub $\ell$-boson stars, are parametrized by an angular momentum number $\ell=(N-1)/2$, an excitation number $n$, and a continuous parameter representing the amplitude of the fields. They are regular at every point and possess a finite total mass. For $\ell = 0$ the standard spherically symmetric boson stars are recovered. We determine their generalizations for $\ell > 0$, and show that they give rise to a large class of new static configurations which might have a much larger compactness ratio than $\ell=0$ stars.