Radiation of Nambu-Goldstone bosons from infinitely long cosmic strings

Nambu-Goldstone-boson radiation from an infinitely long string with a helicoidal standing wave is studied in the weak-field approximation. The radiation power and the spectrum are calculated. In the case of a single-small-amplitude helicoidal standing wave, the radiated power goes as ${\epsilon }^{10}$, indicating that the Nambu-Goldstone-boson radiation mechanism is efficient only for large-amplitude waves. A simple analysis of the radiation due to a wide spectrum of small-amplitude waves indicate that in general the emitted power goes as ${\epsilon }^4$.