Final reheating temperature on a single brane

We make a generic remark on thermal history of a single brane cosmology in models with an infinitely large single extra dimension. We point out that t he reheat temperature of the Universe is bounded by an excess production of gravitons from the thermal bath. The actual bound is given by the brane te nsion. If the initial temperature of the Universe is larger than this bound , then an efficient graviton production shall prevail. However, the brane c ools down gradually as the Kaluza-Klein gravitons take the energy in excess away from the brane. The cooling continues until the radiation dominated p hase is restored, which occurs before the big bang nucleosynthesis. We argu e whatsoever be the early evolution of the Universe, the final radiation do minated phase always starts after the Universe transits from non-convention al era to the standard cosmological era. (C) 2001 Elsevier Science B.V. All rights reserved.