Day 1177

Thursday.

1610.08297
On the hypothesis that cosmological dark matter is composed of intra-light bosons
Hui, Ostriker, Tremaine, Witten

An intriguing alternative to CDM is that the dark matter is a light (m~1e-22 eV) boson having a de Broglie wavelength lambda ~ 1 kpc, oven called fuzzy dark matter (FDM).  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 haloes smaller than about 1e7 (m/1e-22 eV)^-3/2 Msun do not form.  (ii) FDM haloes are comprised of a core that is a stationary, minimum-energy configuration called a "soliton", surrounded by an envelope that resembles a CDM halo.  (iii) The transition between soliton and envelope is determined by a relaxation process analogous to 2-body relaxation in gravitating systems, which proceeds as if the halo were composed of particles with mass ~rho lambda^3 where rho is the halo density.  (iv) Relaxation may have substantial effects on the stellar disk and bulge in the inner parts of disk galaxies.  (v) Relaxation can produce FDM disks but an FDM disk in the solar neighborhood must have a half-thickness of at least 300 (m/1e-22 eV)^-2/3 pc.  (vi) Solitonic FDM sub-haloes evaporate by tunneling through the tidal radius and this limits the minimum sub-halo mass inside 30 kpc of the MW to roughly 1e8 (m/1e-22 eV)^-3/2 Msun.  (vii) If the DM 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 DM is FDM.