Gravitational waves versus cosmic strings

Details Gravitational waves versus cosmic strings Gravitational waves versus cosmic strings

Oct 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jphcs.189a2021k&link_type=abstract

Journal of Physics: Conference Series, Volume 189, Issue 1, pp. 012021 (2009).

Physics

Scientific paper

The equation which governs the temporal evolution of a gravitational wave (GW) in curved space-time can be treated as the Schrodinger equation for a particle moving in the presence of an effective potential. When GWs propagate in an expanding Universe with constant effective potential, there is a critical value (kc) of the comoving wave-number which discriminates the metric perturbations into oscillating (k > kc) and non-oscillating (k < kc) modes. The effective potential is reduced to a non-vanishing constant in a cosmological model which is driven by a two-component fluid, consisting of radiation (dominant) and cosmic strings (subdominant). However, the cosmological evolution (gradually) results in the scaling of any long-cosmic-string network and, therefore, after some time (Δτ) the Universe enters in the pure-radiation epoch. The evolution of the non-oscillatory GW modes during Δτ, results in the distortion of the low-frequency part of the stochastic GW power-spectrum, which, therefore, departs from scale invariance (anticipated in the pure-radiation case). As regards the corresponding high-frequency part (which is determined by the evolution of the oscillating modes), we find that the presence of cosmic strings gives rise to the quantum-gravitational creation of gravitons, leading to the amplification of the GW signal by (almost) two orders of magnitude.

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