The three phases of self-gravitating scalar field ground states

TL;DR

This paper explores how multiple interacting scalar fields in dark matter halos can lead to diverse ground state configurations, challenging the common assumption of universal solitonic cores in ultralight dark matter models.

Contribution

It demonstrates that strong interspecies interactions can cause immiscibility and multiple phases in scalar field ground states, revealing more complex halo structures.

Findings

Sufficiently strong repulsive interactions lead to immiscible phases.

Ground states depend on relative densities, masses, and interactions.

The inner structure of ULDM halos may be more diverse than previously thought.

Abstract

It is generally assumed that scalar field dark matter halos would contain solitonic cores -- spherically symmetric ground state configurations -- at their centers. This is especially interesting in the case of ultralight dark matter (ULDM), where the solitons sizes are on the order of galaxies. In this work, we show that the paradigm of a spherically symmetric soliton embedded in the center of each halo is not universally valid in a scenario with multiple interacting scalar fields. In particular, sufficiently strong repulsive interspecies interactions make the fields immiscible. In such models, the ground state configuration can fall into a number of different phases that depend on the fields' relative densities, masses, and interaction strengths. This raises the possibility that the inner regions of ULDM halos are more complex and diverse than previously assumed.