Almost closing the νMSM sterile neutrino dark matter window with NuSTAR

Abstract

We use NuSTAR observations of the Galactic Center to search for X-ray lines from the radiative decay of sterile neutrino dark matter. Finding no evidence of unknown lines, we set limits on the sterile neutrino mass and mixing angle. In most of the mass range 10-50 keV, these are now the strongest limits, at some masses improving upon previous limits by a factor of ∼ 10. In the νMSM framework, where additional constraints from dark matter production and structure formation apply, the allowed parameter space is reduced by more than half. Future NuSTAR observations may be able to cover much of the remaining parameter space. P r e v io u s X -r a y c o n s t r a in t s M W s a t e ll it e c o u n t s a n d p h a s e s p a c e c o n s t r a in t sNuSTAR GC 2016 FIG. 1. Simplified overview of constraints on νMSM sterile neutrino dark matter in the plane of mass and mixing angle; details are described in Sec. IV, and the experimental constraints included are listed in Fig. 8. For parameters between the gray regions, the observed dark matter abundance can be produced through resonant production in the νMSM. Most of this region is ruled out by constraints from structure formation (blue) or astrophysical X-ray observations (green). Our new constraint (red line and hatched region) is obtained from NuSTAR observations of the GC, and rules out about half of the previously allowed parameter space (white region).

A White Paper on keV sterile neutrino Dark Matter

“…However, in the Galactic Center the flux of the line is also consistent with the expectations for plasma emission lines with no need for a dark matter component [608,610]. We note that the line is also recently detected in the NuStar blank-sky [620] and Galactic center [621] datasets. While it may have an instrumental origin, related to Solar activity [620], it was shown in [620] that in the 'no sun' dataset the line is present with the same intensity, and it appears several times stronger near the Galactic center, as A difficulty in interpreting the origin of a weak emission line is inherent uncertainty in the astrophysical backgrounds, in particular in the flux of plasma emission lines.…”

“…We note in passing that the statement in the recent paper from NuSTAR [621] of these bounds practically closing the parameter space for sterile neutrino Dark Matter is clearly too strong, as such a bound depends on the production mechanism. Since resonant production is driven by the presence of a lepton asymmetry in the primordial plasma that is much larger than the baryon asymmetry, a lower bound on sin 2 (2θ) can in principle be derived by estimating the asymmetry that can realistically be generated [398] and is consistent with known constraints from BBN [261,986].…”

“…Suzaku/XIS 740, 164, 83, 90 [613] Galactic center, Perseus XMM-Newton/EPIC Not specified [614] Perseus Suzaku/XIS 520 [615] Galactic Bulge Suzaku/XIS Not specified [603,616] Milky Way Fermi/GBM 4600 [617] Milky Way Suzaku/XIS 31500 [597] Draco XMM-Newton/EPIC 87 Stacked galaxies XMM-Newton/EPIC 8500 [313] M31 Chandra/ACIS-I 404 [608] M31, Milky Way XMM-Newton/EPIC 1226, 7850 [610] Galactic center, M31 XMM-Newton/EPIC 690, 490 [611] Stacked galaxies XMM-Newton/EPIC 14600 [613] Galactic center XMM-Newton/EPIC Not specified [572] Milky Way Chandra/ACIS 1500 [598] Milky Way Chandra/ACIS-S3 Not specified [485] M31 (12 − 28 off-center) Chandra/ACIS-I 53 [609] Galactic center Chandra/ACIS 751 [611] Stacked galaxies Chandra/ACIS-I 15000 [604,605] Galactic center Suzaku/XIS 190 [615] Galactic Buldge Suzaku/XIS Not specified [617] Milky Way Suzaku/XIS 31500 [602] Milky Way X-ray microcalorimeter 0.1 [601] Milky Way INTEGRAL/SPI 5500 [347] Milky Way INTEGRAL/SPI 12200 [603,616] Milky Way Fermi/GBM 4600 [620] Milky Way NuSTAR 7500 [621] Galactic center NuSTAR 400 Table 9. Summary of existing X-ray observations of DM decays in galaxy clusters and diffuse X-ray background performed by different groups.…”

The upper bound on the lowest mass halo

“…Kennedy et al (2014) investigate the effect of changing the assumed MW mass on the inferred WDM constraints, finding mWDM > 20 keV for MMW < 10 12 M , altogether ruling out some WDM models (e.g. Perez et al 2016). This constraint, however, is extremely sensitive to the parameters of their galaxy formation model, in particular the minimum vmax for a subhalo to be able to cool gas and form a galaxy: changing this from 30 km/s to 25 km/s, their lower bound on mWDM decreases by a factor of 10.…”

Axions, Majorana neutrino masses and implications for the dark sector of the Universe

“…Hence it is much less robust than the upper bound, and can be further relaxed. [26]). The recent analysis of Perez et al [26], employs NuSTAR (Nuclear Spectroscopic Telescope Array) [27] observations of the Galactic Centre, together with additional constraints associated with DM production and its rôle in the structure formation in the Universe, which stem from the requirement that DM comprises predominantly of the lightest of the sterile neutrinos of νMSM.…”