Cosmology with extra dimensions

We review several properties of models that include extra dimensions, focusing on aspects related to cosmology and particle physics phenomenology. The properties of effective four dimensional inflationary geometry are studied in two distinct frameworks: (i) in Kaluza-Klein (KK) compactifications and (ii) in braneworld scenarios. From numerical simulations we find that inflationary braneworlds are unstable if the scale of inflation is too large in comparison with the stabilization scale of the interbrane distance. The analysis of perturbations confirms the existence of a tachyon associated with the volume modulus of the extra dimensions both in braneworlds and KK compactifications. With the numerical program BRANECODE non-perturbative properties of braneworlds are studied. We fully understand the non-perturbative consequences of this instability. Generic attractors are (i) an increase of the interbrane distance and the formation of a naked singularity, (ii) the brane collision, and (iii) the non-linear reconfiguration of the braneworld towards a stable configuration connected with a lower scale of inflation. The most interesting features are understood analytically. In the limit of flat branes, we exactly identify the radion of a two-brane/bulk scalar field system and explore its interactions with the standard model fields located on the branes as one phenomenological consequence. This complex calculation consists of the diagonalization of the five-dimensional Einstein-Hilbert action to second order in the perturbations. Enhanced complexity in comparison to similar calculations performed for the inflaton field in four-dimensional cosmology arises due to the presence of non-trivial boundary conditions. Open questions in cosmology, such as the nature of dark energy and the low power in the quadrupole of the temperature anisotropies of the cosmic microwave background (CMB) radiation, motivate investigations beyond the standard model of cosmology. The simplest generalization of the cosmological constant is provided by a scalar field. We explore the possible dynamics of such scalar fields in the universe at late times. In particular, we focus on their impact on the temperature anisotropies of the CMB. We show that dynamical dark energy does not yield a suppression of power on the largest scales of the CMB for a wide range of potentials.