Cosmological implications of tensor-induced scalar perturbations

Matter-density perturbations can be generated from the non-linear evolution of primordial tensor modes. At second order, we have a mixing between scalar, vector and tensor perturbation modes, we are interested in the second-order scalar perturbations generated by linear tensor modes which are statistically independent of linear scalar modes. Working in the framework of a collisionless cold dark matter plus cosmological constant model and fixing our gauge to the comoving and synchronous one, there are two major objectives investigated in this thesis: First, we study the generation and evolution of second-order energy-density perturbations arising from primordial gravitational waves and their imprint on the matter power spectrum by considering the effect of some high frequency primordial gravitational wave signals. Second, we study the non-Gaussianity of these tensor-induced scalar perturbations, we calculate the Bispectrum as a general expression and in an equilateral shape configuration, These results will have an impact on the potential detectability of such tensorinduced scalar modes on large-scale structure as well as cosmic microwave background anisotropy observables.