After a Global Phase Transition in the early Universe, it is expected that the symmetry-breaking field responsible for it enters into a self-ordering regime. This will generate a new background of Gravitational Waves (GW), and a new source of secondary Non-Gaussian (NG) signatures in the matter fluctuations: textbullet The resulting GW spectrum today is frequency independent (i.e. scale-invariant), with an amplitude greater than that of the GW Background expected from Inflation. For a GUT-scale scenario it turns out to be directly observable by the GW detectors like LIGO, LISA, BBO and DECIGO. textbullet The non-Gaussianity generated is characterized by a distinctive bispectrum with a big amplitude and a very specific spectral form (neither equilateral, nor squeezed). Future observations of the CMB and LSS should thus detect these non-Gaussian signatures or constraint severely the parameters space.

University of Helsinki