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This study examines the validity of the Nambu-Goto approximation used to calculate gravitational waves from cosmic string networks through large-scale lattice field simulations. The researchers found that while the approximation works well for near-global strings, it breaks down significantly for strongly coupled local strings where the vector boson mass to scalar mass ratio approaches unity. The simulations also revealed that particle emission, rather than gravitational wave radiation, dominates energy loss from string networks by a factor of 100 to 1000.
Why it matters
This research is crucial for improving the accuracy of gravitational wave predictions from cosmic strings, which could be detected by current and future gravitational wave observatories. The findings suggest that existing theoretical models may need revision to correctly interpret observational data and assess whether cosmic strings exist in our universe.
Understand the Science
arXiv:2507.00685v2 Announce Type: replace
Abstract: The precise calculation of gravitational wave (GW) from cosmic string networks is of significant theoretical and experimental interest. The Nambu–Goto (NG) approximation has long been employed to calculate GW emission from such networks; however, its validity has never been systematically verified. We perform large-scale zero-temperature Abelian-Higgs lattice simulations under different gauge couplings, and compare them with NG predictions. We find excellent agreement in the power-law region for near-global strings but strong deviation for strongly coupled local strings with $m_v/m_s sim 1$, quantitatively establishing the breakdown of the NG approximation. Additionally, we confirm that particle emission significantly dominates the energy loss of the string network, with the ratio of GW energy to particle energy approximately $10^{-3}$ to $10^{-2}$ for both near-global and local string scenarios.
Source: Testing Nambu-Goto approximation of cosmic string by lattice field simulations