Axionic Co-genesis of Baryon, Dark Matter and Dark Radiation

TL;DR

This paper proposes a unified axion-based mechanism involving coherent oscillations and saxion decay to simultaneously explain dark matter, baryon asymmetry, and dark radiation, aligning with current experimental data.

Contribution

It introduces a novel axionic co-genesis framework that links axion dynamics with baryogenesis and dark matter production in supersymmetric models.

Findings

The mechanism naturally explains the observed dark matter and baryon asymmetry.

It predicts a small dark radiation component consistent with Planck data.

The required supersymmetry breaking scale aligns with the Higgs boson mass.

Abstract

We argue that coherent oscillations of the axion field excited by the misalignment mechanism and non-thermal leptogenesis by the saxion decay can naturally explain the observed abundance of dark matter and baryon asymmetry, thus providing a solution to the baryon-dark matter coincidence problem. The successful axionic co-genesis requires a supersymmetry breaking scale of O(10^{6-7}) GeV, which is consistent with the recently discovered standard-model like Higgs boson of mass about 126 GeV. Although the saxion generically decays into a pair of axions, their abundance sensitively depends on the saxion stabilization mechanism as well as couplings with the Higgs field. We discuss various ways to make the saxion dominantly decay into the right-handed neutrinos rather than into axions, and show that the abundance of axion dark radiation can be naturally as small as \Delta N_{\rm eff} \lesssim {\cal O}(0.1), which is allowed by the Planck data.