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

TL;DR

This paper presents an $SO(10)$ grand unified model predicting axion and WIMP dark matter, proton decay, and inflationary parameters, with testable implications for future cosmological experiments.

Contribution

It introduces a novel $SO(10)$ axion model with stable WIMP-like dark matter and detailed inflationary predictions, addressing domain wall issues and unification.

Findings

Stable WIMP-like dark matter coexists with axion dark matter.

Predicted scalar spectral index $n_s$ between 0.963 and 0.965.

Tensor-to-scalar ratio $r$ between 0.003 and 0.036.

Abstract

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 $Z_2$ 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 $\sim 62.5 \; {\rm GeV}\; (1 \; {\rm 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 $0.963 \lesssim n_s \lesssim 0.965$ and $0.003 \lesssim r \lesssim 0.036$, 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.