Cosmological structure formation and soliton phase transition in fuzzy dark matter with axion self-interactions

Abstract

We investigate cosmological structure formation in Fuzzy Dark Matter (FDM) with an attractive self-interaction (SI) with numerical simulations. Such a SI would arise if the FDM boson were an ultra-light axion, which has a strong CP symmetry-breaking scale (decay constant). Although weak, the attractive SI may be strong enough to counteract the quantum ‘pressure’ and alter structure formation. We find in our simulations that the SI can enhance small-scale structure formation, and soliton cores above a critical mass undergo a phase transition, transforming from dilute to dense solitons.

Cosmology of axion dark matter

“…This result has been confirmed and elaborated on in numerous studies since then, see e.g. [192][193][194][195][196][197][198][199] for a very incomplete sample.…”

“…The fact they cannot merge fast enough is a problem given the number of very massive black holes seen in the centres of modern galaxies. However, orbiting 52One way to circumvent this tension is to add more degrees of freedom to the model, for example by incorporating self-interactions [197,199]. Another possibility could be within an axion model with a large initial misalignment angle which can enhance rather than suppress structure around the Jeans scale [431] 53See e.g.…”

Dark ages, a window on the dark sector. Hunting for ultra-light axions

“…The soliton profile can be modelled as [48] ρ(r) = ρ 0 1 + 0.091 (r/r c ) 2 −8 , where ρ 0 is the central density and r c the radius at which the density reaches half of its central value, For the heavier masses considered, m a ≃ 10 −18 eV, these scales may be accessible by the most futuristic configuration LRAII, for which ℓ cover is of order 10 6 . A proper treatment would require numerical simulations, similar to what has been implemented recently in [50,51].…”

ULDM self-interactions, tidal effects and tunnelling out of satellite galaxies

“…(3.45) in section 3.2.3 in [13], section 5.1.2 in [11] as well as [54,55]). Indeed, there has been a growing interest in recent years to study and constrain self-interactions of scalar field dark matter [14,15,[56][57][58][59][60][61][62][63][64][65][66][67].…”