|DATE||November 11 (Thu), 2021|
|TITLE||Pulsar hints for gravitational waves from cosmic strings?|
|ABSTRACT||All major pulsar timing array (PTA) collaborations?NANOGrav, Parkes PTA, and EPTA?are now seeing indications of a new stochastic process in their latest data sets. If confirmed in the future, this new signal may turn out to be the first glimpse of a stochastic gravitational-wave background at nanohertz frequencies. In this talk, I will review the properties of the new signal and discuss its interpretation in terms of gravitational waves emitted by a network of cosmic strings in the early Universe. I will especially distinguish between stable and metastable cosmic strings, both of which represent realistic and intriguing possibilities in the context of grand unified theories (GUTs). As for metastable cosmic strings, I will present some theoretical advancements in the description of gravitational-wave emission by a decaying cosmic-string network based on recent work in collaboration with Wilfried Buchm?ller and Valerie Domcke [2107.04578]. This will lead to the conclusion that metastable cosmic strings are not only capable of explaining the new PTA signal in the nanohertz band; unlike stable cosmic strings, they also predict a signal within the reach of current-generation ground-based interferometers in the audio band. On their way to design sensitivity, existing gravitational-wave experiments will thus have a realistic chance to probe particle physics processes close to the GUT scale via the observation of gravitational waves from metastable cosmic strings.