Relic abundance of MeV millicharged particles

Abstract

The relic abundance of light millicharged particles (MCPs) with the electric charge $e^{\prime }=5\cdot 10^{-5}e$ and with the mass slightly below or above the electron mass is calculated. The abundance depends on the mass ratio $\eta =m_X/m_e$ and for $\eta <1$ can be high enough to allow MCPs to be the cosmological dark matter or to make a noticeable contribution to it. On the other hand, for $\eta \gtrsim 1$ the cosmological energy density of MCPs can be quite low, ${\Omega }_X{h}_0^2\approx 0.02$ for scalar MCPs, and ${\Omega }_X{h}_0^2\approx 0.001$ for spin 1/2 fermions. But even the lowest value of ${\Omega }_X{h}_0^2$ is in tension with several existing limits on the MCP abundances and parameters. However, these limits have been derived under some natural or reasonable assumptions on the properties of MCPs. If these assumptions are relaxed, a patch in the mass-charge plot of MCPs may appear, permitting them to be dark matter particles.

7 pages, 3 figures; references added; final version published in JETP

References in corpus (8)

• Secluded U(1) below the weak scale
• Forbidden Dark Matter
• An Improved Limit on Invisible Decays of Positronium
• Cosmological Constraints on Very Dark Photons
• Leptophobic Dark Matter at Neutrino Factories
• Scattering of Dark Particles with Light Mediators
• A Milli-Window to Another World
• A balance for Dark Matter bound states

Cited by in corpus (4)

• First Limit on the Direct Detection of Lightly Ionizing Particles for Electric Charge as Low as $e$/1000 with the \textsc{Majorana Demonstrator}
• Passage of millicharged particles in the electron beam-dump: refining constraints from SLACmQ and estimating sensitivity of NA64e
• A balance for Dark Matter bound states
• Constraints on the velocity dispersion of Dark Matter from Cosmology and new bounds on scattering from the Cosmic Dawn