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

Understand

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.