An attractive model: simulating fuzzy dark matter with attractive self-interactions

• Published in: Monthly notices of the Royal Astronomical Society Vol. 533; no. 2; pp. 2454 - 2472
• Main Authors: Painter, Connor A, Boylan-Kolchin, Michael, Mocz, Philip, Vogelsberger, Mark
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01.09.2024
• Subjects: Broken symmetry; Cold dark matter; Dark matter; Decay rate; Dwarf galaxies; Hypothetical particles; Particle decay; Particle physics; Solitary waves; Strong interactions (field theory); galaxies: formation; galaxies: high-redshift; dark matter; cosmology: theory
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stae1912

ABSTRACT Fuzzy dark matter (FDM), comprised of ultralight ($m \sim 10^{-22}\,{\rm eV}$) boson particles, has received significant attention as a viable alternative to cold dark matter (CDM), as it approximates CDM on large scales (${\gtrsim}1$ Mpc) while potentially resolving some of its small-scale problems via kiloparsec-scale quantum interference. However, the most basic FDM model, with one free parameter (the boson mass), is subject to a tension: small boson masses yield the desired cores of dwarf galaxies but underpredict structure in the Lyman-α forest, while large boson masses render FDM effectively identical to CDM. This Catch-22 problem may be alleviated by considering an axion-like particle with attractive particle self-interactions. We simulate an idealized FDM halo with self-interactions parametrized by an energy decay constant $f \sim 10^{15}~\rm {GeV}$ related to the axion symmetry-breaking conjectured to solve the strong-CP problem in particle physics. We observe solitons, a hallmark of FDM, condensing within a broader halo envelope, and find that the density profile and soliton mass depend on self-interaction strength. We propose generalized formulae to extend those from previous works to include self-interactions. We also investigate a critical mass threshold predicted for strong interactions at which the soliton collapses into a compact, unresolved state. We find that the collapse happens quickly, and its effects are initially contained to the central region of the halo.