Towards microscopic ab initio calculations of astrophysical SS-factors

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 3/2−3/2− and 1/2−1/2− bound states in 7Be as well as the many-body scattering states in the 1/2+1/2+, 3/2+3/2+ and 5/2+5/2+ channels are calculated as eigenstates of the same microscopic effective Hamiltonian. Finally the SS-factor is calculated from E1E1 transition matrix elements between the many-body scattering and bound states. For 3He(αα, γγ)7Be the SS-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(αα, γγ)7Li reaction the calculated SS-factor is about 15% above the data.