Gravitational-Wave Stochastic Background from Kinks and Cusps on Cosmic Strings

TL;DR

This study shows that kinks on cosmic-string loops contribute to the gravitational-wave stochastic background at the same order as cusps. By deriving the metric perturbations from the Nambu-Goto string EMT and computing the cusp and kink radiation, the authors provide analytic and numerical results for both small- and large-loop regimes, revealing flat high-frequency spectra once cosmological redshift and beaming are accounted for. The work translates into concrete prospects for detection by LIGO, LISA, and pulsar-timing bounds, and delineates the parameter space ($G\mu$, $p$, and $\alpha$) constrained by BBN, CMB, and astrophysical observations. Overall, kinks strengthen the case for cosmic strings as a detectable source of stochastic gravitational waves and help refine the complementary bounds on string tension and reconnection probability.

Abstract

We compute the contribution of kinks on cosmic string loops to stochastic background of gravitational waves (SBGW).We find that kinks contribute at the same order as cusps to the SBGW.We discuss the accessibility of the total background due to kinks as well as cusps to current and planned gravitational wave detectors, as well as to the big bang nucleosynthesis (BBN), the cosmic microwave background (CMB), and pulsar timing constraints. As in the case of cusps, we find that current data from interferometric gravitational wave detectors, such as LIGO, are sensitive to areas of parameter space of cosmic string models complementary to those accessible to pulsar, BBN, and CMB bounds.

Figures (3)

• Figure 1: Kink and Cusp spectrum for small loops: (1) $G\mu=2 \times 10^{-6}$, $p=10^{-3}$ and $\epsilon=10^{-4}$, (2) $G\mu=10^{-7}$, $p=5\times10^{-3}$ and $\epsilon=1$ .
• Figure 2: Kink and Cusp spectrum for large loops: (1) $G\mu= 10^{-7}$ and $p=5\times 10^{-3}$, (2) $G\mu=10^{-9}$ and $p=5\times 10^{-2}$.
• Figure 3: Top-left: Accessible regions in the $\varepsilon-G\mu$ plane for $p = 10^{-3}$ for small loops (loop sizes are determined by gravitational back-reaction). Top-right: Same as above for $p=10^{-2}$. Bottom-left: Same as above for $p=10^{-1}$. Bottom-right: Accessible regions in the $p-G\mu$ plane for the large long-lived loop models. The accessible regions are to the right of the corresponding curves. All models are within reach of LISA and advanced LIGO, and most are within the projected pulsar bound.