Constraints on sterile neutrino dark matter

We present a comprehensive analysis of constraints on the sterile neutrino as a dark matter candidate. The minimal production scenario with a standard thermal history and negligible cosmological lepton number is in conflict with conservative radiative decay constraints from the cosmic X-ray background in combination with stringent small-scale structure limits from the Lyman-alpha forest. We show that entropy release through massive particle decay after production does not alleviate these constraints. We further show that radiative decay constraints from local group dwarf galaxies are subject to large uncertainties in the dark matter density profile of these systems. Within the strongest set of constraints, resonant production of cold sterile neutrino dark matter in nonzero lepton number cosmologies remains allowed.

Figure 1

Full parameter space constraints for the sterile neutrino production models, assuming sterile neutrinos constitute the dark matter. Contours labeled with lepton number $L=0$, $L=0.003$, $L=0.01$, $L=0.1$ are production predictions for constant comoving density of ${\Omega }_s=0.24$ for $L=0$, and ${\Omega }_s=0.3$ for nonzero $L$ [12]. Constraints from X-ray observations include the diffuse X-ray background (green) [27], from XMM-Newton observations of the Coma and Virgo clusters (light blue) [28]. The diagonal wide-hatched region is the claimed potential constraint from XMM-Newton observations of the LMC [29]. The region at $m_s<0.4\mathrm{keV}$ is ruled out by a conservative application of the Tremaine-Gunn bound [14]. The regions labeled $\mathrm{Ly}\alpha$ are those from the amplitude and slope of matter power spectrum inferred from the SDSS $\mathrm{Ly}\alpha$ forest [$\mathrm{Ly}\alpha$ (1)] [21], using high-resolution $\mathrm{Ly}\alpha$ data [$\mathrm{Ly}\alpha$ (2)] [20, 21], and that from the high-$z$ SDSS $\mathrm{Ly}\alpha$ of SMMT [$\mathrm{Ly}\alpha$ (3)] [22]. The gray region to the right of the $L=0$ case is where sterile neutrino dark matter is overproduced. Also shown is the horizontal band of the mass scale consistent with producing a 100–300 pc core in the Fornax dwarf galaxy [64]. The parameters consistent with pulsar kick generation are in horizontal hatching [38, 39, 40].

Figure 2

The value of the quantity $J[\Delta \Omega (\theta )]$ (see text) for two representative dark matter distributions in the Draco dwarf galaxy. The thickness of both curves corresponds to the range of values in each profile due to the distance uncertainties to Draco. The top curve corresponds to an NFW profile with $\log ({\rho }_s/M_{\odot }{\mathrm{kpc}}^{-3})=7.0$ and $\log (r_s/\mathrm{kpc})=0.85$, while the lower curve depicts a Burkert profile with $\log ({\rho }_s/M_{\odot }{\mathrm{kpc}}^{-3})=9.0$ and $\log (r_s/\mathrm{kpc})=-0.75$.

Figure 3

Shown here are the constraints on the massive particle decay dilution model. The diagonally-hatched (blue) region is the lower-mass $\mathrm{Ly}\alpha$ limit of Ref. 21, while the vertically (red) hatched region the $\mathrm{Ly}\alpha$ limit of SMMT. In combination with the conservative XRB limit (green) [27], even extreme dilution models of $S=100$ are in conflict with combined constraints. The standard case of no dilution corresponds to $S=1$.