Towards microscopic ab initio calculations of astrophysical [formula omitted]-factors

Abstract

Low energy capture cross sections are calculated within a microscopic many-body approach using an effective Hamiltonian derived from the Argonne V18 potential. The dynamics is treated within Fermionic Molecular Dynamics (FMD) which uses a Gaussian wave-packet basis to represent the many-body states. A phase-shift equivalent effective interaction derived within the Unitary Correlation Operator Method (UCOM) that treats explicitly short-range central and tensor correlations is employed. As a first application the 3He(α,γ) 7Be reaction is presented. Within the FMD approach the microscopic many-body wave functions of the 3 / 2 − and 1 / 2 − bound states in 7Be as well as the many-body scattering states in the 1 / 2 + , 3 / 2 + and 5 / 2 + channels are calculated as eigenstates of the same microscopic effective Hamiltonian. Finally the S -factor is calculated from E 1 transition matrix elements between the many-body scattering and bound states. For 3He( α , γ ) 7Be the S -factor agrees very well, both in absolute normalization and energy dependence, with the recent experimental data from the Weizmann, LUNA, Seattle and ERNA experiments. For the 3H( α , γ ) 7Li reaction the calculated S -factor is about 15% above the data.