A WDM model for the evolution of galactic halos

TL;DR

This paper proposes a warm dark matter model with keV-mass particles that explains galactic halo structures and aligns with sterile neutrino candidates, contrasting with cold dark matter predictions.

Contribution

It introduces a Vlasov particle-based warm dark matter model that predicts halo cusps at finite distances, supported by N-body simulations and consistent with sterile neutrino properties.

Findings

Particles have a typical velocity of ~330 km/s.

Halo cusps form at finite distances from galactic centers.

Sterile neutrinos are plausible dark matter candidates.

Abstract

It is a well-known fact that the gravitational effect of dark matter in galaxies is only noticeable when the orbital accelerations drop below $a_0 \simeq 2\times 10^{-8}$ cm s$^{-1}$ (Milgrom's Law). This peculiarity of the dynamic behaviour of galaxies was initially ascribed to a modification of Newtonian dynamics (MOND theory) and, consequently, it was used as an argument to criticize the dark matter hypothesis. In our model, warm dark matter is composed by collisionless Vlasov particles with a primordial typical velocity $\simeq 330$ km s$^{-1}$ and, consequently, they evaporated from galactic cores and reorganized in halos with a cusp at a finite distance from the galactic center (in contrast with Cold Dark Matter simulations which predict a cusp at the center of galaxies). This is confirmed by mean-field N-body simulations of the self-gravitating Vlasov dark matter particles in the potential well of the baryonic core. The rest mass of these particles, $\mu$, is determined from a kinetic theory of the early universe with a cosmological constant. We find that $\mu$ is in the range of a few keV. This result makes sterile neutrinos the best suited candidates for the main component of dark matter.