The cosmological 7Li problem from a nuclear physics perspective

The primordial abundance of ⁷Li as predicted by Big Bang Nucleosynthesis (BBN) is more than a factor 2 larger than what has been observed in metal-poor halo stars. Herein, we analyze the possibility that this discrepancy originates from incorrect assumptions about the nuclear reaction cross sections relevant for BBN. To do this, we introduce an efficient method to calculate the changes in the ⁷Li abundance produced by arbitrary (temperature dependent) modifications of the nuclear reaction rates. Then, considering that ⁷Li is mainly produced from ⁷Be via the electron capture process ⁷Be+e^- → ⁷Li+ν_e, we assess the impact of the various channels of ⁷Be destruction. Differently from previous analysis, we consider the role of unknown resonances by using a complete formalism which takes into account the effect of Coulomb and centrifugal barrier penetration and that does not rely on the use of the narrow-resonance approximation. As a result of this, the possibility of a nuclear physics solution to the ⁷Li problem is significantly suppressed. Given the present experimental and theoretical constraints, it is unlikely that the ⁷Be+n destruction rate is underestimated by the 2.5 factor required to solve the problem. We exclude, moreover, that resonant destruction in the channels ⁷Be+t and ⁷Be+³He can explain the ⁷Li puzzle. New unknown resonances in ⁷Be+d and ⁷Be+α could potentially produce significant effects. Recent experimental results have ruled out such a possibility for ⁷Be+d. On the other hand, for the ⁷Be+α channel very favorable conditions are required. The possible existence of a partially suitable resonant level in ¹¹C is studied in the framework of a coupled-channel model and the possibility of a direct measurement is considered.