Core Fragmentation in Simplest Superfluid Dark Matter Scenario

TL;DR

This paper investigates galactic halo structures in a superfluid dark matter model with self-interactions, revealing core fragmentation into droplets and revising interaction bounds based on degeneracy effects, implying ultra-light particles are necessary.

Contribution

It introduces the impact of superfluid phase transition and fragmentation in dark matter halos, and revises self-interaction constraints considering degeneracy effects.

Findings

Galactic cores can fragment into superfluid droplets due to Jeans instability.

Degeneracy enhances interaction rates, affecting bounds on self-interaction cross sections.

Ultra-light dark matter particles are required for kpc-size superfluid solitons within observational constraints.

Abstract

We study the structure of galactic halos within a scalar dark matter model, endowed with a repulsive quartic self-interaction, capable of undergoing the superfluid phase transition in high-density regions. We demonstrate that the thermalized cores are prone to fragmentation into superfluid droplets due to the Jeans instability. Furthermore, since cores of astrophysical size may be generated only when most of the particles comprising the halo reside in a highly degenerate phase-space, the well-known bound on the dark matter self-interaction cross section inferred from the collision of clusters needs to be revised, accounting for the enhancement of the interaction rate due to degeneracy. As a result, generation of kpc-size superfluid solitons, within the parameter subspace consistent with the Bullet Cluster bound, requires dark matter particles to be ultra-light.