We study in a self-consistent way the impact of the emission of bulk gravitons on the (homogeneous) cosmology of a three-brane embedded in a five-dimensional spacetime. In the low energy regime, we recover the well known result that the bulk affects the Friedmann equation only via a radiationlike term $\mathcal{C}/a^4$, called dark or Weyl radiation. In the high energy regime, we find that the Weyl parameter $\mathcal{C}$ is no longer constant but grows rapidly. Consequently, $\mathcal{C}$ today is determined by the past history of the brane universe and depends on the number of relativistic degrees of freedom at the high/low energy transition.

• Received 27 June 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.171301