1Primordial Gravitational Waves from Inflation and Preheating

There are at least three cosmic backgrounds of primordial gravitational waves coming from inflation: those produced during inflation and associated with the stretching of quantum modes; those produced at the violent stage of preheating after inflation; and those associated with the self-ordering of Goldstone modes if inflation ends via a global symmetry breaking scenario, like in hybrid inflation. Each background has its own characteristic spectrum with specific features. We describe in detail the origin of extra peaks in the PGW background from preheating in the case in which inflation ends with the formation of cosmic strings due to an Abelian Higgs model after hybrid inflation. We then discuss the prospects for detecting each gravitational wave background, and distinguishing between them with a very sensitive probe, the local B-mode of the cosmic microwave background polarization. Cosmological Inflation1), 2) naturally generates a spectrum of density fluctua-tions responsible for large scale structure formation which is consistent with the observed CMB anisotropies.3) It also generates a spectrum of gravitational waves, whose amplitude is directly related to the energy scale during inflation and whic