Revisiting metastable cosmic string breaking

Metastable cosmic strings appear in models of new physics with a two-step symmetry breaking G → H → 1, where π1(H) ≠ 0 and π1(G) = 0. They decay via the monopole-antimonopole pair creation inside. Conventionally, the breaking rate has been estimated by an infinitely thin string approximation, which requires a large hierarchy between the symmetry breaking scales. In this paper, we reexamine it by taking into account the finite sizes of both the cosmic string and the monopole. We obtain a robust lower limit on the tunneling factor e^{−S_B} even for regimes the conventional estimate is unreliable. In particular, it is relevant to the cosmic string interpretation of the gravitational wave signals recently reported by pulsar timing array experiments.

Akifumi Chitose, Masahiro Ibe, Yuhei Nakayama, Satoshi Shirai, Keiichi Watanabe