BBN and CMB Constraints on Dark Radiation Revisited

The effect of dark radiation on BBN and CMB has been studied earlier. We revised the study, since new data has been available for light element abundances and Plank has new and improved data on CMB. We study the effect of an additional term dervied by integrating the Einstein equation in the 5-dimensional Randall-Sundrum Model. This new term scales as ${a^-4}$ and hence the term 'radiation'. This term is the constant of integration and it can be either positve or negative. Dark radiation can have significant effects on light element abundances at the end of big bang nucleosynthesis (BBN) and on angular spectrum of cosmic microwave background (CMB). We take $\rho_{Dr}$ to be between -41.5$\%$ and +70$\%$ of $\rho_\gamma$ and the corresponding changes in BBN abundances and CMB spectrum are observed. In this new analysis we find that $\rho_{dr}$/$\rho_\gamma$ has a preference for positive dark radiation.