Sterile Neutrino Dark Matter Constrained

A new paper largely rules out sterile neutrino dark matter with sterile neutrinos having masses of less than 4,000 eV. Active neutrinos can't be much more than 0.5 eV, almost ten thousand times less massive than that. It also presses up against hard upper bounds on the mass of warm dark matter particles, never mind that warm dark matter models with sterile dark matter particles have been shown to produce dark matter distributions inconsistent with what is observed.

This paper is one more cut in the death of a thousand cuts that dark matter particle theories are experiencing. 

Low-mass galaxies provide a powerful tool with which to investigate departures from the standard cosmological paradigm in models that suppress the abundance of small dark matter structures. One of the simplest metrics that can be used to compare different models is the abundance of satellite galaxies in the Milky Way. Viable dark matter models must produce enough substructure to host the observed number of Galactic satellites. 

Here, we scrutinize the predictions of the neutrino Minimal Standard Model (νMSM), a well-motivated extension of the Standard Model of particle physics in which the production of sterile neutrino dark matter is resonantly enhanced by a lepton asymmetry in the primordial plasma. This process enables the model to evade current constraints associated with non-resonantly produced dark matter. 

Independently of assumptions about galaxy formation physics we rule out, with at least 95 per cent confidence, all parameterizations of the νMSM with sterile neutrino rest mass, Ms ≤ 1.4keV. Incorporating physically motivated prescriptions of baryonic processes and modelling the effects of reionization strengthen our constraints, and we exclude all νMSM parameterizations with Ms ≤ 4keV. Unlike other literature, our fiducial constraints do not rule out the putative 3.55 keV X-ray line, if it is indeed produced by the decay of a sterile neutrino; however, some of the most favoured parameter space is excluded. 

If the Milky Way satellite count is higher than we assume, or if the Milky Way halo is less massive than M(MW)(200) = 8×10^11 M⊙, we rule out the νMSM as the origin of the 3.55 keV excess. 

In contrast with other work, we find that the constraints from satellite counts are substantially weaker than those reported from X-ray non-detections.

Oliver Newton, et al., "Constraints on the properties of νMSM dark matter using the satellite galaxies of the Milky Way" arXiv:2408.16042 (August 28, 2024).

Another study finds that gravitino dark matter would have to have masses in the range of 1 TeV or greater (possibly much greater) which has myriad problems of its own, largely ruling out this dark matter candidate as a practical matter.