Cold dark matter plus not-so-clumpy dark relics

Abstract

Abstract. Various particle physics models suggest that, besides the (nearly) cold dark matter that accounts for current observations, additional but sub-dominant dark relics might exist. These could be warm, hot, or even contribute as dark radiation. We present here a comprehensive study of two-component dark matter scenarios, where the first component is assumed to be cold, and the second is a non-cold thermal relic. Considering the cases where the non-cold dark matter species could be either a fermion or a boson, we derive consistent upper limits on the non-cold dark relic energy density for a very large range of velocity dispersions, covering the entire range from dark radiation to cold dark matter. To this end, we employ the latest Planck Cosmic Microwave Background data, the recent BOSS DR11 and other Baryon Acoustic Oscillation measurements, and also constraints on the number of Milky Way satellites, the latter of which provides a measure of the suppression of the matter power spectrum at the smallest scales due to the free-streaming of the non-cold dark matter component. We present the results on the fraction f ncdm of non-cold dark matter with respect to the total dark matter for different ranges of the non-cold dark matter masses. We find that the 2σ limits for non-cold dark matter particles with masses in the range 1-10 keV are f ncdm ≤ 0.29 (0.23) for fermions (bosons), and for masses in the 10-100 keV range they are f ncdm ≤ 0.43 (0.45), respectively.

Hiding an elephant: heavy sterile neutrino with large mixing angle does not contradict cosmology

“…Therefore, only some part of DM can be generated here. A rough constraint on this part can be obtained from [28], but we do not present a detailed analysis here (in our case this constraint is always satisfied once the sterile neutrino fraction does not exceed roughly one third).…”

Dark matter shifts away from direct detection

“…For dark photon masses that satisfy the overclosure bound of Eq. (33) the relevant observables are CMB and BAO measurements, while the MW satellite count becomes important at higher masses, of order keV [53]. In the region m γ D 1 eV, where the dark photon behaved as radiation at photon decoupling, the constraints shown in Fig.…”

“…(34) can be compared with the bounds given in Ref. [53], after correcting for the fact that there the non-cold relic was assumed to have temperature equal to that of the SM neutrinos, hence the mass needs to be rescaled by a factor T γ D /T ν ≈ 0.52. The result is shown in Fig.…”

keV sterile neutrino with large mixing angle is still alive

“…2 where sterile neutrinos contribute more than 30% of total DM. This region is prohibited because sterile neutrinos are too warm according to [18]. As seen from Fig.…”

“…Black line corresponds to non-resonant production of Ω N = Ω DM . In regions dashed by white (left panel) and black (right panel) inclined lines sterile neutrinos contribute no more than 30% of the whole DM -this fraction of warm component is already prohibited by[18]. White space region in the upper right corner breaks X-ray constraint(14) and, therefore, is unreachable in the model with phase transition.…”