Seminar detail: Decay rates of GUT-scale metastable cosmic strings and the nanohertz gravitational-wave background

Date&Time	Tue Oct 27 2026 (17:00 - 18:00)
Speaker	Yu Hamada
Affiliation	Osaka University
Title	Decay rates of GUT-scale metastable cosmic strings and the nanohertz gravitational-wave background
Abstract	In 2023, pulsar timing array (PTA) experiments reported evidence for a stochastic gravitational-wave background at nanohertz frequencies. Interpreting this signal in terms of metastable cosmic strings typically points to the GUT scale. Connecting the signal to GUT models requires an accurate determination of the string decay rate, but conventional estimates rely on the thin-string approximation and carry substantial uncertainties. In this talk, I will discuss a method for computing the decay rate beyond this approximation in a simple model with two-step symmetry breaking $SU(2)\to U(1)\to 1$. I will show how these corrections affect the gravitational-wave spectrum and the interpretation of the PTA signal, and discuss prospects for embedding this setup in GUT models and distinguishing between SO(10) and E_6 GUTs using metastable cosmic strings.
Remarks
Slide/Video