Ultralight scalars as cosmological dark matter

By L. Hui, Jeremiah P. Ostriker, S. Tremaine, E. Witten. 2016

1,277 citations recorded by the source corpus.

Many aspects of the large-scale structure of the Universe can be described successfully using cosmological models in which 27±1% of the critical mass-energy density consists of cold dark matter (CDM). However, few—if any—of the predictions of CDM models have been successful on scales of ∼10 kpc or less. This lack of success is usually explained by the difficulty of modeling baryonic physics (star formation, supernova and black-hole feedback, etc.). An intriguing alternative to CDM is that the dark matter is an extremely light (m∼10-22 eV) boson having a de Broglie wavelength λ∼1 kpc, often called fuzzy dark matter (FDM). We describe the arguments from particle physics that motivate FDM, review previous work on its astrophysical signatures, and analyze several unexplored aspects of its behavior. In particular, (i) FDM halos or subhalos smaller than about 107(m/10-22 eV)-3/2 M⊙ do not form, and the abundance of halos smaller than a few times 1010(m/10-22 eV)-4/3 M⊙ is substantially smaller in FDM than in CDM. (ii) FDM halos are comprised of a central core that is a stationary, minimum-energy solution of the Schrodinger-Poisson equation, sometimes called a “soliton,” surrounded by an envelope that resembles a CDM halo. The soliton can produce a distinct signature in the rotation curves of FDM-dominated systems. (iii) The transition between soliton and envelope is determined by a relaxation process analogous to two-body relaxation in gravitating N-body systems, which proceeds as if the halo were composed of particles with mass ∼ρλ3 where ρ is the halo density. (iv) Relaxation may have substantial effects on the stellar disk and bulge in the inner parts of disk galaxies, but has negligible effect on disk thickening or globular cluster disruption near the solar radius. (v) Relaxation can produce FDM disks but a FDM disk in the solar neighborhood must have a half-thickness of at least ∼300(m/10-22 eV)-2/3 pc and a midplane density less than 0.2(m/10-22 eV)2/3 times the baryonic disk density. (vi) Solitonic FDM subhalos evaporate by tunneling through the tidal radius and this limits the minimum subhalo mass inside ∼30 kpc of the Milky Way to a few times 108(m/10-22 eV)-3/2 M⊙. (vii) If the dark matter in the Fornax dwarf galaxy is composed of CDM, most of the globular clusters observed in that galaxy should have long ago spiraled to its center, and this problem is resolved if the dark matter is FDM. (viii) FDM delays galaxy formation relative to CDM but its galaxy-formation history is consistent with current observations of high-redshift galaxies and the late reionization observed by Planck. If the dark matter is composed of FDM, most observations favor a particle mass ≳10-22 eV and the most significant observational consequences occur if the mass is in the range 1–10×10-22 eV. There is tension with observations of the Lyman-α forest, which favor m≳10–20×10-22 eV and we discuss whether more sophisticated models of reionization may resolve this tension.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b66458939d8bd0d3c6c4722c34549ea9442c956f

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Citations in the corpus

Using the Full Power of the Cosmic Microwave Background to Probe Axion Dark Matter (2017, methodology): “1017 GeV, where fa is the axion “decay constant”, ULAs contribute at the percent level to the cosmic critical density (Marsh 2016; Hui et al. 2017).”
Recent Progress in the Physics of Axions and Axion-Like Particles (2020, background): “3), often the corresponding PQ symmetries are broken only by non-perturbative effects [4, 44, 49, 64], yielding V ∝ e−b/g2 ∗ for some coupling g∗.”
Constraining the mass of light bosonic dark matter using SDSS Lyman-α forest (2017, neutral): “Hu et al. (2000); Marsh (2016b); Hui et al. (2017).”
The GALAH survey and Gaia DR2: dissecting the stellar disc’s phase space by age, action, chemistry, and location (2018, background): “Then, we would have conclusive evidence that dark matter comprises nondegenerate fermions (Bœhm & Fayet 2004) rather than being an artefact introduced by using the wrong theory of gravity (Milgrom & Sanders 2008) or being a bosonic condensate of an ultralight quantum field (q.v. Hui et al. 2017).”
The Simons Observatory: science goals and forecasts (2018, background): “…mass ∼ 10−7 eV but its much lighter cousin, the ULA, with masses between 10−33 < ma/eV < 10 −22 (Amendola and Barbieri 2006; Arvanitaki et al. 2010a; Hui et al. 2017) The light end of the mass range are axions that exhibit dark-energy-like behavior, while the axions with masses ma ≥ 10−27 eV…”
The Kreuzer-Skarke axiverse (2018, neutral): “lated with ˝ last \ d ). Note that by (4.20), \ last 6= ˝ last(t\ d ). 15Many authors use the term ‘ultralight axion’ for axions with m& 10 33 eV that could make up part of the dark matter, as in [24,25]. We avoid the term ‘ultralight’ when speaking of the far lighter axions found here, with m˝1”
Hunting for the Dark Matter Wake Induced by the Large Magellanic Cloud (2019, methodology): “For example, Hui et al. (2017) showed that the orbital decay times of globular clusters in the Fornax dwarf galaxy are longer in the FDM model.”
Constraints on Dark Matter Microphysics from the Milky Way Satellite Population (2019, background): “Non-standard DM scenarios, such as warm DM (WDM; Abazajian 2017; Adhikari et al. 2017) and fuzzy DM (FDM; Hu et al. 2000; Hui et al. 2017), often involve smoothing of matter perturbations and suppression of structure on small scales.”
Superradiance (2015, background): “Note that in the 10−21 eV range ultralight bosons are also compelling dark-matter candidates [646].”
Detecting fundamental fields with LISA observations of gravitational waves from extreme mass-ratio inspirals (2021, neutral): “The corrections to the Kerr metric depend on the dimensionless parameter ζ ≡ α Mn = q α μn , (7)”