Boson Star from Repulsive Light Scalars and Gravitational Waves

TL;DR

This paper explores how ultra-light scalar dark matter with repulsive self-interactions influences boson star properties, revealing the importance of full curved space-time equations and complex potentials for understanding maximum mass and gravitational wave signals.

Contribution

It demonstrates the significance of solving full equations in curved space-time for boson star stability and highlights the impact of complex scalar potentials on star properties and gravitational wave detection.

Findings

Maximum mass depends on full curved space-time equations.

Backreaction can turn repulsion into effective attraction.

Complex potentials alter boson star characteristics and GW signals.

Abstract

We study properties of boson stars consisting of ultra-light scalar dark matter with repulsive self-interactions. We investigate the origin of the maximum mass of spherically symmetric stable stars which emerges only when solving the full equations of motion in curved space-time, but not when solving the approximated Schr\"odinger-Newton equations. When the repulsion is weak, the backreaction of the curvature on the scalars acts as an additional source of attraction and can overcome the repulsion, resulting in a maximum star mass and compactness. We also point out that the potential in a UV completed particle physics model of light scalar dark matter is generally more complicated than the widely used $\phi^4$ interaction. Additional interactions beyond $\phi^4$ in the potential can dramatically change the properties of boson stars as well as modify the prospect of LIGO gravitational wave detection for binary mergers of boson stars.