Earth-bound Milli-charge Relics

TL;DR

This paper explores how millicharged particles can accumulate inside Earth, leading to enhanced densities and new detection possibilities through their interactions, annihilation signatures, and bound state formations.

Contribution

It provides a detailed analysis of mCP accumulation, thermalization, and potential detection methods, introducing novel experimental approaches for millicharged particle searches.

Findings

Millicharged particles can thermalize and build up inside Earth.

Density enhancements of up to 10^14 times the galactic abundance are possible.

New detection signatures include annihilation signals and bound state formations.

Abstract

Dark sector particles with small electric charge, or millicharge, (mCPs) may lead to a variety of diverse phenomena in particle physics, astrophysics and cosmology. Assuming their possible existence, we investigate the accumulation and propagation of mCPs in matter, specifically inside the Earth. Even small values of millicharge lead to sizeable scattering cross sections on atoms, resulting in complete thermalization, and as a consequence, considerable build-up of number densities of mCPs, especially for the values of masses of GeV and higher when the evaporation becomes inhibited. Enhancement of mCP densities compared to their galactic abundance, that can be as big as $10^{14}$, leads to the possibility of new experimental probes for this model. The annihilation of pairs of mCPs will result in new signatures for the large volume detectors (such as Super-Kamiokande). Formation of bound states of negatively charged mCPs with nuclei can be observed by direct dark matter detection experiments. A unique probe of mCP can be developed using underground electrostatic accelerators that can directly accelerate mCPs above the experimental thresholds of direct dark matter detection experiments.