Speaker

Oliver Newton

Centre for Theoretical Physics PAS

Abstract

Low-mass galaxies are powerful tools with which to investigate departures from the standard cosmological paradigm in models that suppress the abundance of small dark matter substructures. 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 lepton asymmetry in the primordial plasma. This extra degree of freedom allows the model to evade current constraints on the mass of thermally produced dark matter. Independently of assumptions about galaxy formation physics we rule out, with at least 95 per cent confidence, all parametrizations of the νMSM with Ms ≤ 1 keV, independently of other model parameters and of the Milky Way halo mass. Incorporating physically motivated prescriptions of baryonic processes and modelling the effects of reionization strengthens our constraints and we exclude all models with Ms ≤ 3 keV. 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. We find that the constraints from satellite counts are substantially weaker than those reported from X-ray non-detections.

Scientific theme

Dark matter constraints, Milky Way satellites, dwarf galaxies