Reheating the Universe in braneworld cosmological models with bulk-brane energy transfer

Abstract

The emergence of the cosmological composition (the reheating era) after the inflationary period is analyzed in the framework of the braneworld models, in which our Universe is a 3-brane embedded in a five-dimensional bulk, by assuming the possibility of brane-bulk energy exchange. The inflaton field is assumed to decay into normal matter only, while the dark matter is injected into the brane from the bulk. To describe the reheating process we adopt a phenomenological approach, by describing the decay of the inflaton field using a friction term proportional to the energy density of the field. After the radiation dominated epoch the model reduces to the standard four-dimensional cosmological model. The modified field equations are analyzed analytically and numerically in both the extra-dimension dominated reheating phase (when the quadratic terms in energy density dominate the dynamics) and the general case. The evolution profiles of the matter, of the scalar field and of the scale factor of the Universe are obtained for different values of the parameters of the model and of the equations of state of the normal and dark matter. The equation describing the time evolution of the ratio of the energy densities of the dark and the normal matter is also obtained. The ratio depends on the rate of energy flow between the bulk and the brane. The observational constraint of an approximately constant ratio of the dark and the baryonic matter requires that the dark matter must be non-relativistic (cold). The model predicts a reheating temperature of the order of 3 × 10 6GeV, a brane tension of the order of 10 25GeV 4, and the composition of the Universe obtained is consistent with the observational data. © 2008 IOP Publishing Ltd.