http://arxiv.org/abs/1709.03845
If cosmic strings are formed in the early universe, their associated loops emit gravitational waves during the whole cosmic history and contribute to the stochastic gravitational wave background at all frequencies. We provide a new estimate of the stochastic gravitational wave spectrum taking into account various effects neglected so far. In particular, we consider a realistic cosmological loop distribution, in scaling, as it can be inferred from Nambu-Goto numerical simulations. We include both gravitational wave emission and backreaction effects on the loop distribution and show that they produce two distinct features in the spectrum. Concerning the string microstructure, in addition to the presence of cusps and kinks, we show that gravitational wave bursts created by the collision of kinks could dominate the signal for wiggly strings, a situation which may be favoured in the light of recent numerical simulations. In view of these new results, we propose three prototypical scenarios, within the margin of the remaining theoretical uncertainties, for which we derive the corresponding signal and estimate the constraints on the string tension put by both the LIGO and European Pulsar Timing Array (EPTA) observations. The less constrained of these scenarios has a smooth microstructure and is shown to have a string tension GU < 7.2 x 10^{-11}, at 95% of confidence. The most constrained model describes very kinky loops and satisfies GU < 6.7 x 10^{-14}, at 95% of confidence.
C. Ringeval and T. Suyama
Wed, 13 Sep 17
63/72
Comments: 32 pages, 11 figures, uses jcappub