Narrow Results

There is a significant discrepancy between the current theoretical prediction of the cosmological lithium abundance, mostly produced as ⁷Be during the Big Bang, and its observationally inferred value. We investigate whether the resonant enhancement of ⁷ Be burning reactions may alleviate this discrepancy. We identify one narrow nuclear level in ⁹B, E_5/2⁺ ≃ 16.7 MeV that is not sufficiently studied experimentally, and being just ~ 200 keV above the ⁷Be+d threshold, may lead to the resonant enhancement of ⁷Be(d, γ)⁹B and ⁷Be(d, p)αα reactions. We determine the relationship between the domain of resonant energies E_r and the deuterium separation width Γ_d that results in the significant depletion of the cosmological lithium abundance and find that (E_r, Γ_d)≃(170-220, 10-40) keV can eliminate the current discrepancy. Such a large width at this resonant energy can be only achieved if the interaction radius for the deuterium entrance channel is very large, a₂₇ ≥ 10 fm. New nuclear experimental and theoretical work is needed to clarify the role this resonance plays on the BBN prediction of the lithium abundance. Alternatively, the most liberal interpretation of the allowed parameters of 16.7 MeV resonance can significantly increase the errors in predicted lithium abundance: [⁷Li/H]_BBN = (2.5-6) × 10^-10.

The light elements and their isotopes were produced during standard big bang nucleosynthesis (SBBN) during the first minutes after the creation of the universe. Comparing the calculated abundances of these light species with observed abundances, it appears that all species match very well except for lithium (⁷Li) which is overproduced by the SBBN. This discrepancy is rather challenging for several reasons to be considered on astrophysical and on nuclear physics ground, or by invoking nonstandard assumptions which are the focus of this paper. In particular, we consider a variation of the chemical potentials of the neutrinos and their temperature. In addition, we investigated the effect of dark matter on ⁷Li production. We argue that including nonstandard assumptions can lead to a significant reduction of the ⁷Li abundance compared to that of SBBN. This aspect of lithium production in the early universe may help to resolve the outstanding cosmological lithium problem.

Big Bang Nucleosynthesis (BBN) requires several nuclear physics inputs and nuclear reaction rates. An up-to-date compilation of direct cross sections of $\mathrm{\text{d(d, p)t}}$, ${\mathrm{\text{d(d, n)}}}^3$He and ${}^3\mathrm{\text{He}}{(\mathrm{\text{d, p}})}^4$He reactions is given, being these ones among the most uncertain bare-nucleus cross sections. An intense experimental effort has been carried on in the last decade to apply the Trojan Horse Method (THM) to study reactions of relevance for the BBN and measure their astrophysical S(E)-factor. The reaction rates and the relative error for the four reactions of interest are then numerically calculated in the temperature ranges of relevance for BBN $(0.01<{\mathrm{\text{T}}}_9<10)$. These value were then used as input physics for primordial nucleosynthesis calculations in order to evaluate their impact on the calculated primordial abundances and isotopical composition for H, He and Li. New results on the ${}^7\mathrm{\text{Be}}{(\mathrm{\text{n}},\alpha )}^4$He reaction rate were also taken into account.These were compared with the observational primordial abundance estimates in different astrophysical sites. Reactions to be studied in perspective will also be discussed.