Abstract
We measure properties of dark matter in four well motivated scenarios: fermions with ultra-relativistic thermal equilibrium (URTE), bosons with URTE, fermions with non-relativistic thermal equilibrium (NRTE), and bosons with NRTE. We attempt to discriminate between these four scenarios with studies of spiral galaxy rotation curves, and galaxy stellar mass distributions. The measurements show evidence for boson dark matter with a significance of 3.5σ, and obtain no significant discrimination between URTE and NRTE.
Highlights
Non-relativistic dark matter in the early universe has a density ρh (a) that scales as a−3, and a particle root-mean-square velocity vhrms (a) that scales as a−1, where a is the expansion parameter. (Throughout, the sub-index “h”stands for the halo of dark matter.) Note that vhrms (a) ρh (a)1 3 is an adiabatic invariant independent of a
For bosons with ultra-relativistic thermal equilibrium (URTE) or non-relativistic thermal equilibrium (NRTE), there is a tail at large k due to the excess of low momentum dark matter particles in the limit μ′ → −0
We assume that dark matter is in thermal and diffusive equilibrium with the standard model sector in the early universe, and decouples while still ultra-relativistic
Summary
Non-relativistic dark matter in the early universe has a density ρh (a) that scales as a−3 , and a particle root-mean-square (rms) velocity vhrms (a) that scales as a−1 , where a is the expansion parameter. Stands for the halo of dark matter.) Note that vhrms (a) ρh (a) is an adiabatic invariant independent of a. Consider a free observer in a density peak. This observer feels no gravity, observes dark matter expanding adiabatically, reaching maximum expansion, and collapsing adiabatically into the core of a galaxy. Note that adiabatic expansion implies ( ) ( ) = vhrms a ( ) ( ) ( ) ρh a 1 3. Where 3 vr2h 1 2 is the root-mean-square velocity of dark matter particles in the core of the galaxy, and ρh (r → 0) is the density of dark matter in the core of the galaxy. (We use the standard notation in cosmology as defined in [1].)
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