Big Bang Nucleosynthesis with an Evolving Radion in the Brane World Scenario

We consider the big bang nucleosynthesis (BBN) in the Brane world scenario, where all matter fields are confined on our 3-brane and the radion of the Brane evolves cosmologically. In the Einstein frame fundamental fermion masses vary and the results of standard BBN (SBBN) are modified. We can thus use the observational primordial element abundances to impose constraints on the possible variations of the radion. The possibility of using the evolving radion to resolve the discrepancies between the Wilkinson Microwave Anisotropy Probe (WMAP) and SBBN values of the baryon-to-photon ratio ($\eta$) is also discussed. The results and constraints presented here are applicable to other models in which fundamental fermion masses vary.