Small scale aspects of warm dark matter: Power spectra and acoustic oscillations

Abstract

We provide a semi-analytic study of the small scale aspects of the power spectra of warm dark matter (WDM) candidates that decoupled while relativistic with arbitrary distribution functions. These are characterized by two widely different scales k eq ∼ 0.01 (Mpc) −1 and k f s = √ 3 k eq /2 V 2 eq 1 2with V 2 eq 1 2 ≪ 1 the velocity dispersion at matter radiation equality. Density perturbations evolve through three stages: radiation domination when the particle is relativistic and non-relativistic and matter domination. An early ISW effect during the first stage leads to an enhancement of density perturbations and a plateau in the transfer function for k k f s . An effective fluid description emerges at small scales which includes the effects of free streaming in initial conditions and inhomogeneities. The transfer function features WDM-acoustic oscillations at scales k 2 k f s . We study the power spectra for two models of sterile neutrinos with m ∼ keV produced nonresonantly, at the QCD and EW scales respectively. The latter case yields acoustic oscillations on mass scales ∼ 10 8 M ⊙ . Our results reveal a quasi-degeneracy between the mass, distribution function and decoupling temperature suggesting caveats on the constraints on the mass of a sterile neutrino from current WDM N-body simulations and Lyman-α forest data. A simple analytic interpolation of the power spectra between large and small scales and its numerical implementation is given.

Improved limits on sterile neutrino dark matter using full-sky Fermi Gamma-ray Burst Monitor data

“…[19][20][21][22][23][24] for some of the scenarios). Sterile neutrinos could be a warm or cold dark matter candidate [25][26][27][28][29]. In addition, some sterile neutrino dark matter models can explain the baryon asymmetry in the Universe [30][31][32][33].…”

AdS braneworld with backreaction

“…In spite of the large-scale successes of cold DM there is still some unresolved issues such as overproduction of small scale structure and halos with a central cusp [26]. These problems are somewhat alleviated by warm DM and in particular by sterile neutrino warm DM [27,28]. However, a recent analysis [29] shows that a realistic warm DM scenario with DM 4 keV in agreement with recent constraints from Lyman-α forest [30] is not able to alleviate the small scale crisis of cold DM structure formation.…”

Constraining models for keV sterile neutrinos by quasidegenerate active neutrinos

“…While the condition to correctly form cosmological structure rules out hot (highly relativistic) DM [2,3], the other two possibilities of cold (nonrelativistic) or warm (moderately relativistic) DM are still consistent with all constraints. Apart from weakly interacting massive particles (WIMPs), which are generic cold DM candidates, the case of particle warm or cold DM with a mass of a few keV has attracted the interest of the structure formation simulation community [4,5,6,7,8,9,10], too. In addition, this was fueled by model-independent analyses [11,12] and surveys like ALFALFA [13], which suggest the possibility of keV-DM.…”