Solar fusion and Big Bang nucleosynthesis from ab initio theory

Solar fusion and Big Bang nucleosynthesis from ab initio theory: The ³He(α,γ)⁷Be and ³H(α,γ)⁷Li radiative-capture processes hold great astrophysical significance. Their reaction rates between ∼20 and 500 keV are essential to calculate the primordial ⁷Li abundance in the universe. In addition, standard solar model predictions for the fraction of pp-chain branches resulting in ⁷Be versus ⁸B neutrinos depend critically on the ³He(α,γ)⁷Be astrophysical S factor at about 20 keV. These capture cross sections are strongly suppressed at such low energies and thus hard to measure in a laboratory. As reported in Physics Letters B (2016), TRIUMF nuclear theorists investigated these reactions ab initio using a chiral nucleon–nucleon interaction. Our calculated ³He(α,γ)⁷Be cross sections agree reasonably with the higher-energy experimental data including those measured at TRIUMF while the ³H(α,γ)⁷Li ones are overestimated. Our low-energy predictions help reduce uncertainty of nuclear data evaluations for astrophysics.