Objectives of the proposal
Investigating the physics of the early Universe is the great goal of cosmology and fundamental physics. The CMB is certainly the most powerful and natural tool to constrain models of particle physics at energies which will be never reached by laboratory experiments and to trace new physics beyond the standard model. In particular, the detection of tensor perturbations of the space-time metric, which lead to a primordial gravitational wave background – PGWB, is a smoking gun for the inflationary theory of the early universe. The PGWB imprints a unique pattern (the so called B-modes) in the polarization of CMB photons. Therefore, the primary scientific exploitation of CMB B-mode data aims to a definitive probe of the inflation paradigm and to an estimate of the energy scale at which inflation occurs. Another crucial observable to probe the physical mechanism behind inflation is primordial non-Gaussianity (PNG), in that it allows to test the interactions among quantum fields during inflation and, along with PGWB, it can also distinguish among very different mechanisms and models. Finally, it must be underlined that the observation of the microwave sky is important also for astrophysical and fundamental physics problems that are of interest per se and that are on the frontier of current research: Galactic foregrounds, physics of galaxy clusters, gravitational lensing as a probe of the dark matter, astrophysics of point sources, neutrino physics and, not to be forgotten, the issue of the CMB spectral distortions. All these aspects are strongly interconnected and it is difficult to have a breakthrough without considering them all.