Revisiting metastable cosmic string breaking

Metastable cosmic strings, appearing in models with two-step symmetry breaking (G → H → 1, where π₁ (H) ≠ 0 and π₁ (G) = 0), decay via monopole-antimonopole pair creation. The conventional breaking rate estimation uses an infinitely thin string approximation, requiring a large hierarchy between symmetry breaking scales. This paper re-examines this, considering finite cosmic string and monopole sizes. A robust lower limit on the tunneling factor is obtained, even where the conventional estimate is unreliable, relevant to the gravitational wave signals from pulsar timing array experiments.

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