Neutralino dark matter stars can not exist

TL;DR

This paper demonstrates that stable, pure neutralino dark matter stars cannot exist because neutralinos cannot reach thermal equilibrium and cannot be supported by Fermi pressure, implying most dark matter in such stars must be standard particles.

Contribution

It provides a theoretical analysis showing that neutralino-based dark matter stars are impossible due to equilibrium and support constraints, using the Oppenheimer-Volkoff equation.

Findings

Neutralino cross sections are comparable, preventing thermal equilibrium.

Neutralino stars cannot be supported by Fermi pressure.

Most of the mass in such objects must be standard model particles.

Abstract

Motivated by the recent "Cosmos Project" observation of dark-matter concentrations with no ordinary matter in the same place, we study the question of the existence of compact objects made of pure dark matter. We assume that the dark matter is neutralino, and compare its elastic and annihilation cross sections. We find that the two cross sections are of the same order of magnitude. This result has a straightforward and important consequence that neutralinos comprising a compact object can not achieve thermal equilibrium. To substantiate our arguments, by solving Oppenheimer-Volkoff equation we constructed a model of the star made of pure neutralinos. We explicitly showed that the condition for the thermal equilibrium supported by the Fermi pressure is never fulfilled inside the star. This neutralino state can not be described by the Fermi-Dirac distribution. Thus, a stable neutralino star, which is supported by the Fermi pressure, can not exist. We also estimated that a stable star can not contain more than a few percents of neutralinos, most of the mass must be in the form of the standard model particles.