A Parallel World in the Dark

TL;DR

This paper proposes a dark parallel world model that explains the coincidence of dark matter and dark radiation densities, predicts sterile neutrinos and self-interacting dark matter, and offers testable relations between dark radiation and sterile neutrinos.

Contribution

It introduces a dark sector model with a parallel world that naturally addresses dark matter and dark radiation coincidences, predicting observable sterile neutrinos and dark matter properties.

Findings

Predicts a sterile neutrino with mass 0.1-1 eV

Establishes a relation between dark radiation and sterile neutrino abundance

Suggests self-interacting dark matter from the dark baryons

Abstract

The baryon-dark matter coincidence is a long-standing issue. Interestingly, the recent observations suggest the presence of dark radiation, which, if confirmed, would pose another coincidence problem of why the density of dark radiation is comparable to that of photons. These striking coincidences may be traced back to the dark sector with particle contents and interactions that are quite similar, if not identical, to the standard model: a dark parallel world. It naturally solves the coincidence problems of dark matter and dark radiation, and predicts a sterile neutrino(s) with mass of ${\cal O}(0.1 - 1)$\,eV, as well as self-interacting dark matter made of the counterpart of ordinary baryons. We find a robust prediction for the relation between the abundance of dark radiation and the sterile neutrino, which can serve as the smoking-gun evidence of the dark parallel world.