Hydrodynamics of galactic dark matter

TL;DR

This paper models galactic dark matter halos as self-gravitating, self-interacting gases within General Relativity, deriving constraints on particle masses compatible with observed rotation curves and including candidates like neutralinos and axinos.

Contribution

It introduces a relativistic hydrodynamical model of dark matter halos that links observable rotation curves to particle physics constraints.

Findings

Compatible with universal rotation curves under non-relativistic Maxwell-Boltzmann assumptions.

Derives a minimal particle mass bound between 30 eV and 60 eV.

Includes candidate particles such as neutralinos, axinos, and keV-scale particles.

Abstract

We consider simple hydrodynamical models of galactic dark matter in which the galactic halo is a self-gravitating and self-interacting gas that dominates the dynamics of the galaxy. Modeling this halo as a sphericaly symmetric and static perfect fluid satisfying the field equations of General Relativity, visible barionic matter can be treated as ``test particles'' in the geometry of this field. We show that the assumption of an empirical ``universal rotation curve'' that fits a wide variety of galaxies is compatible, under suitable approximations, with state variables characteristic of a non-relativistic Maxwell-Boltzmann gas that becomes an isothermal sphere in the Newtonian limit. Consistency criteria lead to a minimal bound for particle masses in the range $30 \hbox{eV} \leq m \leq 60 \hbox{eV}$ and to a constraint between the central temperature and the particles mass. The allowed mass range includes popular supersymmetric particle candidates, such as the neutralino, axino and gravitino, as well as lighter particles ($m\approx$ keV) proposed by numerical N-body simulations associated with self-interactive CDM and WDM structure formation theories.