Precise measurements of neutron lifetime and big bang nucleosynthesis

In this talk, we review the current status of the relationships between measurements of neutron lifetime and predictions of light element abundances in big-bang nucleosynthesis (BBN). Performing the Monte Carlo simulation with experimental errors in neutron life-time and nuclear reaction rates in the computation, we can estimate the uncertainties of the prediction of primordial value of D, 4He and 7Li. In BBN, especially 4He is the most sensitive element to the neutron lifetime. Recently it was reported that neutron lifetime was measured within 0.1% (τn=885.7 ± 0.8) accuracy. In this situation, we can determine the primordial value of the 4He mass fraction within 0.1% accuracy. (author)