Effect of the neutron lifetime on processes in the early Universe

The influence of the neutron lifetime on the abundance of light elements produced during the primordial nucleosynthesis early in the birth of the Universe is considered. Among light elements, namely, D, $^3$He, $^{4}$He, and $^{7}$Li, $^{4}$He proves to be most sensitive to neutron lifetime $\tau_n$. Astronomic data on the light element abundance also provide the best accuracy for $^{4}$He. The solution of a number of problems discussed in this paper requires improving the accuracy of observations for the 4He abundance and refining the value of $\tau_n$.