  In this Thesis I discuss several recent results obtained using the CMB
spectra measured by Planck and several other cosmological probes. Extensions of
the $\Lambda$CDM model are studied, including the presence of an additional
sterile neutrino (motivated by the short-baseline oscillation anomalies) and of
a thermal axion. The degeneracies of the cosmological effects of these
particles with the power spectrum of primordial perturbations are tested. We
also show that the power spectrum of initial scalar perturbations can be
degenerate with the presence of primordial non-Gaussianities, thus affecting
the constraints on the non-Gaussianity parameter $f_{NL}$. Finally, an
effective interaction between dark energy and dark matter is studied.
