Off-shell effects in the energy dependence of the Be7(p,gamma)B8 astrophysical S factor

Abstract

I show that off-shell effects, like antisymmetrization and Be-7 distortions, can significantly influence the energy dependence of the nonresonant Be7(p,gamma)B8 astrophysical S factor at higher energies. The proper treatment of these effects results in a vitrually flat E1 component of the S factor at E_cm = 0.3-1.5 MeV energies in the present eight-body model. The energy dependence of the nonresonant S factor, predicted by the present model, is in agreement with the low-energy direct capture data and the existing high-energy Coulomb dissociation data. Irrespective of whether or not the present energy dependence is correct, off-shell effects can cause 15--20% changes in the value of S(0) extrapolated from high-energy (E_cm > 0.7 MeV) data.