Re-examining the Lithium abundance problem in Big-Bang nucleosynthesis

Abstract

One of the three testaments in favor of the big bang theory is the prediction of the primordial elemental abundances in the big-bang nucleosynthesis (BBN). The Standard BBN is a parameter-free theory due to the precise knowledge of the baryon-to-photon ratio of the Universe obtained from studies of the anisotropies of cosmic microwave background radiation. Although the computed abundances of light elements during primordial nucleosynthesis and those determined from observations are in good agreement throughout a range of nine orders of magnitude, there is still a disparity of ${}^7$Li abundance overestimated by a factor of $\sim 2.5$ when calculated theoretically. The number of light neutrino flavors, the neutron lifetime and the baryon-to-photon ratio in addition to the astrophysical nuclear reaction rates determine the primordial abundances. We previously looked into the impact of updating baryon-to-photon ratio and neutron lifetime and changing quite a few reaction rates on the yields of light element abundances in BBN. In this work, calculations are performed using new reaction rates for ${}^3$H(p, $\gamma$)${}^4$He, ${}^6$Li(p, $\gamma$)${}^7$Be, ${}^7$Be(p, $\gamma$)${}^8$B, ¹³N(p, $\gamma$)¹⁴O, ${}^7$Li(n, $\gamma$)${}^8$Li and ¹¹B(n, $\gamma$)¹²B along with the latest measured value of neutron lifetime. We observe from theoretical calculations that these changes result in improvement by causing further reduction in the abundance of ${}^7$Li than calculated earlier.