Probing GUTs and SUSY with Gravitational Waves from Metastable Cosmic Strings

by Stefan Antusch

Monday 1 Dec 2025, 14:00 → 16:00 Europe/Berlin

Pulsar timing arrays (PTAs) have recently reported first evidence for a stochastic gravitational wave (GW) background at nanohertz frequencies, with metastable cosmic strings providing one of the best-fitting explanations. Under the assumption that the PTA results originate from metastable cosmic strings, we analyse the potential of present and future GW observatories for probing the change of particle degrees of freedom caused, e.g., by a supersymmetric (SUSY) extension of the Standard Model (SM). We find that signs of the characteristic doubling of degrees of freedom predicted by SUSY could be detected at Einstein Telescope and Cosmic Explorer even if the masses of the SUSY partner particles are as high as about $10^4$ TeV, far above the reach of any currently envisioned particle collider. We also discuss the detection prospects for the case that some entropy production, e.g. from a late decaying modulus field inducing a temporary matter domination phase in the evolution of the universe, somewhat dilutes the GW spectrum, delaying discovery of the stochastic GW background at LIGO-Virgo-KAGRA. We furthermore discuss the generation of metastable cosmic strings from the multi-step breaking of GUT symmetry, and how the PTA results allow to identify promising classes of SO(10) GUT models.