Gravitational waves from melting cosmic strings

Appearance of cosmic strings in the early Universe is a common manifestation of new physics typically linked to some high energy scale. In this paper, we discuss a different situation, where a model underlying cosmic string formation is approximately scale free. String tension is naturally related to the square of the temperature of the hot primordial plasma in such a setting, and hence decreases with (cosmic) time. With gravitational backreaction neglected, the dynamics of these melting strings in an expanding Universe is equivalent to the dynamics of constant tension strings in a Minkowski spacetime. We provide an estimate for the emission of gravitational waves from string loops. Contrary to the standard case, the resulting spectrum is markedly non-flat and has a characteristic falloff at frequencies below the peak one. The peak frequency is defined by the underlying model and lies in the range accessible by the future detectors for very weak couplings involved.

Automated summary

The appearance of cosmic strings is a common phenomenon in the early Universe, usually associated with high energy scales. This paper discusses a different scenario where the formation of cosmic strings is approximately scale free. The dynamics of these melting strings in an expanding Universe is equivalent to that of constant tension strings in a Minkowski spacetime, and the resulting spectrum of gravitational waves from string loops is non-flat and exhibits a characteristic falloff at frequencies below the peak one.