Constraints on neutrino masses from WMAP5 and BBN in the lepton asymmetric universe

In this paper,we put constraints on neutrino properties such as mass m(nu) and degeneracy parameters xi(i) from WMAP5 data and light element abundances by using a Markov chain Monte Carlo (MCMC) approach. In order to take consistently into account the effects of the degeneracy parameters, we run the Big Bang Nucleosynthesis code for each value of xi(i) and the other cosmological parameters to estimate the Helium abundance, which is then used to calculate CMB anisotropy spectra in stead of treating it as a free parameter. We find that the constraint on m(nu) is fairly robust and does not vary very much even if the lepton asymmetry is allowed, and is given by Sigma m(nu) < 1.3eV (95% C.L.).