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Prediction of the primordial abundances of elements in the big-bangnucleosynthesis (BBN) is one of the three strong evidences for the big bangmodel. Precise knowledge of the baryon-to-photon ratio of the Universe fromobservations of the anisotropies of cosmic microwave background radiation hasmade the Standard BBN a parameter-free theory. Although, there is a goodagreement over a range of nine orders of magnitude between abundances of lightelements deduced from observations and calculated in primordialnucleosynthesis, there remains a yet-unexplained discrepancy of $^7$Liabundance higher by a factor of $\sim 3$ when calculated theoretically. Theprimordial abundances depend on the astrophysical nuclear reaction rates and onthree additional parameters, the number of light neutrino flavours, the neutronlifetime and the baryon-to-photon ratio in the universe. The effect of themodification of thirty-five reaction rates on light element abundance yields inBBN was investigated earlier by us. In the present work we have incorporatedthe most recent values of neutron lifetime and the baryon-to-photon ratio andfurther modified $^3$He($^4$He,$\gamma$)$^7$Be reaction rate which is useddirectly for estimating the formation of $^7$Li as a result of $\beta^+$ decayas well as the reaction rates for t($^4$He,$\gamma$)$^7$Li andd($^4$He,$\gamma$)$^6$Li. We find that these modifications reduce thetheoretically calculated abundance of $^7$Li by $\sim 12\%$.

Primordial lithium abundance problem of BBN and baryonic density in the universe