Hubble law and brane matter after ekpyrosis

We study brane matter in the ekpyrotic scenario and observe that in order t o obtain standard gravity on the visible brane, the tension of the visible brane should be positive. If the sizes of both the fifth dimension and the Calabi-Yau threefold are fixed, the Israel junction conditions do not allow time-dependent brane matter. Relaxing this constraint, it is possible to o btain approximately standard cosmology on the visible brane, with small cor rections due to possible time-dependence of the Calabi-Yau threefold. (C) 2 001 Published by Elsevier Science B.V.