In this talk, we show how it is possible to constrain fundamental physics with cosmology, using Cosmic Microwave Background (CMB) temperature and polarization anisotropies in combination with other cosmological datasets and other observations.

We start deriving new constraints on the neutron lifetime. Under the assumption of standard Big Bang Nucleo- synthesis, the abundance of light elements, in particular Helium, is strongly dependent on this quantity. From CMB anisotropies it is possible to constrain primordial abundances of light elements, inferring the value of the neutron lifetime. We start considering recent Planck 2015 results of temperature and polarization anisotropies of the CMB. We show how including direct astrophysical measurements of primordial Helium abundance it is possible to obtain stringent constraints on the neutron lifetime. Furthermore, we compute the neutron lifetime theoretical expectation and we compare this value with our results, with the value quoted by the Particle Data Group and with the ones obtained in “bottle method” and “beam method” experiments. Finally, we perform forecasts on different future CMB experiments.

With CMB temperature and polarization anisotropies it is also possible to constrain a Cosmological Gravitational Waves Background (CGWB). The origin of this background is still unkown, but it can be measured or evaluated in differente ways. In particular, if it has adiabiatic initial conditions, it will behave as extra radiation and contribute to the total amount of radiative energy density. It is possible to parametrize this contribution as extra relativistic degrees of freedom and put strong limits on it using measurements of CMB anisotropies and primordial abundances of light elements. We update previews results considering Planck 2015 release and other recent experiments.