The existence of a primordial spectrum of gravitational waves is a generic prediction of inflation, and several CMB experiments are going after their signatures. Here I will discuss how the coupling of a pseudoscalar inflaton to a gauge field can induce, in a two-step process, gravitational waves with unusual properties such as: (i) a net chirality (ii) a blue spectrum (iii) being detectable in the (relatively) near future by ground-based gravitational interferometers (iv) large nongaussianities even if the scalar perturbations are approximately gaussian.

University of Massachusetts, Amherst