Explaining PTA Results by Metastable Cosmic Strings from SO(10) GUT

TL;DR

This paper links recent PTA gravitational wave observations to a specific SO(10) GUT model with metastable cosmic strings, detailing how the model's symmetry breaking scales align with the observed GW spectrum.

Contribution

It provides a detailed analysis of a supersymmetric SO(10) GUT model that naturally produces metastable cosmic strings consistent with PTA GW data, integrating inflation and neutrino mass generation.

Findings

The model's symmetry breaking scales match PTA GW frequencies.

Metastable cosmic strings from the model can explain the stochastic GW background.

Gauge coupling unification constrains the GUT breaking scales.

Abstract

In a recent paper (see https://doi.org/10.1103/PhysRevD.108.095053), we have demonstrated that the 2023 PTA results, which hint at a stochastic gravitational wave (GW) background at nanohertz frequencies, point towards a promising model-building route for realizing $SO(10)$ Grand Unification with embedded inflation. The proposed supersymmetric scenario solves the doublet-triplet splitting without fine-tuning, accounts for charged fermion and neutrino masses, avoids conflicts with current proton decay bounds, and includes only representations no larger than the adjoint. It features multi-step breaking of $SO(10)$ to the Standard Model gauge symmetry, with inflation embedded such that metastable cosmic strings are produced at the end of inflation. This cosmic string network generates a stochastic GW background that can explain the PTA results. In this paper, we provide a detailed analysis of the singled out GUT model class, focusing on how the gauge coupling unification condition affects the scales of multi-step $SO(10)$ breaking and the preferred GW spectra. The lowest breaking scale, linked to inflation, the generation of right-handed neutrino masses for the seesaw mechanism, and metastable cosmic string production, coincides with the range suggested by the PTA results.