Composite neutrinos and the QCD axion: baryogenesis, dark matter, small Dirac neutrino masses, and vanishing neutron EDM

Abstract

We consider a chiral gauge theory from which light composite Dirac neutrinos dynamically emerge, augmented by a QCD axion to solve the strong CP problem. We show that an interplay between the composite sector and the axion can also simultaneously lead to successful baryogenesis and generate a correct dark matter abundance via "co-genesis" without contradicting present constraints. We predict $\hat{I}”N_{\mathrm{eff}}\ge 0.14$ and $m_a$ in the range $O(1)\hat{\mathrm{I}}¼\mathrm{eV}$--$O(10)\mathrm{meV}$, which can be firmly tested by upcoming CMB experiments and axion searches.

10 pages, 1 figure, v2: minor changes, version accepted by Phys. Rev. D