Particle and gravitational wave emission from cosmic string loops

Cosmic strings are one-dimensional topological defects predicted to form in the early universe after a phase transition by a variety of extensions of the Standard Model, ranging from axion models to grand-unified theories. After forming, strings are expected to decay via the emission of both particles and gravitational waves (GWs), leading to the formation of a GW background (GWB) that may be detected by ongoing or future GW experiments. Traditionally, predictions of the GWB produced by cosmic strings are based on the Nambu-Goto (NG) approximation, in  which the internal structure of the strings and their decay into particles are neglected. However, a correct interpretation of a positive GW signal would require of accurate predictions beyond the NG approximation that fully account for the field-theoretic nature of cosmic strings. In this talk I describe how the dynamics of cosmic strings can be simulated using field-theory lattice simulations, and how we have used such simulations to characterize the emission of particles and GWs from closed cosmic strings, called loops. Our results show that, contrary to NG expectations, cosmic string loops with lengths up to 10^5 times their core width decay predominantly via particle emission, with negligible poduction of GWs, with no indication that this behaviour may change for longer strings. We expect thee results will lead to a significant reduction of current predictions for the amplitude of the GWB produced by cosmic-string networks.