Speaker
Maxime Grandjean
(VUB)
Description
Metastable strings can arise because of a two-step symmetry breaking chain of the type $SU(2)\to U(1)\to 1$. These strings can decay via quantum tunnelling through the nucleation of monopole anti-monopole pairs, and have recently been considered as candidates for explaining the gravitational-wave background observed by pulsar timing arrays. In our work, we study the classical stability of such metastable strings in a concrete model realizing this symmetry breaking pattern. We identify regions of parameter space in which the string solutions are classically stable or unstable. Our results show that classical instabilities can impact the parameter space relevant for explaining the PTA signal.