Axions, WIMPs, proton decay and observable r in SO(10)

We explore some experimentally testable predictions of an SO(10) axion model which includes two 10-plets of fermions in order to resolve the axion domain wall problem. The axion symmetry can be safely broken after inflation, so that the isocurvature perturbations associated with the axion field are negligibly small. An unbroken gauge Z2 symmetry in SO(10) ensures the presence of a stable WIMP-like dark matter, a linear combination of the electroweak doublets in the fermion 10-plets and an SO(10) singlet fermion with mass similar to 62.5 GeV (1 TeV) when it is mostly the singlet (doublet) fermion, that co-exists with axion dark matter. We also discuss gauge coupling unification, proton decay, inflation with non-minimal coupling to gravity and leptogenesis. With the identification of the SM singlet Higgs field in the 126 representation of SO(10) as inflaton, the magnetic monopoles are inflated away, and we find 0.963 less than or similar to n(s) less than or similar to 0.965 and 0.003 less than or similar to r less than or similar to 0.036, where n(s) and r denote the scalar spectral index and tensor-to-scalar ratio, respectively. These predictions can be tested in future experiments such as CMB-S4.

Automated summary

In this paper, we explore experimentally testable predictions of an SO(10) axion model with two 10-plets of fermions to address the axion domain wall problem. The model allows for the safe breaking of axion symmetry after inflation, resulting in negligible isocurvature perturbations. An unbroken gauge Z2 symmetry in SO(10) guarantees the presence of stable dark matter, which is a combination of electroweak doublets and an SO(10) singlet fermion. Other topics discussed include gauge coupling unification, proton decay, inflation with non-minimal coupling to gravity, and leptogenesis. The predictions made in this paper can be tested in future experiments, such as CMB-S4.