Comment on “keV neutrino dark matter in a fast expanding universe” by Biswas et al.

Fernandez, Nicolas  (Department of Physics, University of California Santa Cruz, 1156 High St., Santa Cruz, CA, 95064, USA) (Santa Cruz Institute for Particle Physics, 1156 High St., Santa Cruz, CA, 95064, USA) ; Profumo, Stefano (Department of Physics, University of California Santa Cruz, 1156 High St., Santa Cruz, CA, 95064, USA) (Santa Cruz Institute for Particle Physics, 1156 High St., Santa Cruz, CA, 95064, USA)

04 January 2019

Abstract: Biswas et al. [1] found that the thermal relic density of a dark matter particle freezing out while the universe's energy density is dominated by a non-standard extra component ϕ , whose energy density redshifts faster than radiation, can be greatly suppressed. Here we show that this result, which contradicts extensive previous literature, is incorrect: the mistake lies with the assumption that the (decoupled) extra component ϕ contributes to the entropic degrees of freedom relevant for dark matter freeze out. If this were the case, a completely different approach would be needed to calculate the dark matter relic abundance, with dramatically different results.


Published in: Physics letters B (2019)
Published by: Elsevier
DOI: 10.1016/j.physletb.2018.12.057
License: CC-BY-3.0



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