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arXiv · 2608.31163

Evolution of Cosmic String Loops under Gravitational Backreaction

Lasse Gerblich·Richard A. Battye·E. P. S. Shellard
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Abstract

Nambu-Goto cosmic string loops generically develop cusps, points where the string momentarily reaches the speed of light. These cusps produce strong gravitational wave bursts with a characteristic strain spectrum $\tilde{h}(\omega)\propto (G\mu)\,\omega^{-4/3}$, making them prime targets for gravitational wave searches, where $\mu$ is the string mass per unit length. However, this picture is modified when one accounts for gravitational backreaction. Using a convenient gauge, we reformulate the Nambu-Goto equations of motion for a loop moving in its own dynamically sourced gravitational field, enabling the first continuous numerical evolution of loops under this backreaction. A key finding is that locally cusps survive backreaction. Nevertheless, the gravitational waveform calculated in this formalism is significantly modified, weakening the cusp burst and introducing a high-frequency cutoff at $f_c\propto(G\mu)^{-3/2}$. This suppression above $f_c$ reduces the expected signal-to-noise ratio in current and near-future detectors relative to unperturbed waveform predictions.

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Lasse Gerblich, Richard A. Battye, E. P. S. Shellard. 2026-08-31. Evolution of Cosmic String Loops under Gravitational Backreaction. https://arxiv.org/abs/2608.31163

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