Two-Brane Models and BBN

We obtain a class of solutions for the AdS$_5$ two-brane models by imposing the observed value of cosmological constant and Newton coupling constant on the visible brane. When all terms up to the first order of matter density are included, the cosmological evolution on the observable brane depends on the equation of state of the matter and consequently when the pressure exists, the cosmology of these models deviates from FLRW cosmology. We show that it is possible to choose the matter equation of state on the hidden brane to neutralize its contribution on the cosmological evolution of the visible brane. We compare the prediction of these models for primordial {\it $^4$He} yield with observations. In standard BBN with $n_{\nu}^{light} = 3$ this brane model is ruled out. If in addition to 3 SM neutrinos there is one light sterile neutrino, this model reconciles the observed {\it $^4$He} yield with a high ${\Omega}_b \sim 0.033 h^{-2}$ suggested by BOOMERANG and MAXIMA experiments.