Late-time phase transition and the galactic halo as a Bose liquid

We consider the ultralight pseudo Nambu-Goldstone boson appearing in the late-time cosmological phase tansition theories as a major dark matter candidate. Since it is almost massless, its nature is more wavelike than particlelike. We study quantum mechanically how they from a galactic halo. Three predictions are made: (i) the mass profile ρ∼${\mathit{r}}^{\mathrm{-}1.6}$; (ii) there are ripplelike fine structures in the rotation curve; (iii) the rotation velocity multiplied by the ripple’s wavelength is galaxy independent.