Gravitational Waves from Cosmic Strings

Gravitational waves from cosmic strings are generated in the first fractions of a second after the Big Bang, potentially providing a unprecedented probe of the early universe. We discuss the key dynamical processes underlying calculations of the stochastic background produced by a string network and we detail the parameter dependencies of the resulting spectral density Ωgr(f). The present constraints on the cosmic string mass scale µ arising from the millisecond pulsar timings and primordial nucleosynthesis are discussed, justifying our present conservative bound Gµ/c 2 < 5.4(±1.1) × 10 −6. We then discuss the strong prospect of detecting (or ruling out) cosmic string background with the next generation of gravitational wave experiments. Comparison is also made with alternative cosmological sources of gravitational waves such as inflation and hybrid topological defects.