Towards Microscopic Ab Initio Calculations of Astrophysical S-Factors

TL;DR

This paper presents a microscopic many-body approach using Fermionic Molecular Dynamics and effective interactions to calculate astrophysical S-factors for low energy nuclear reactions, achieving good agreement with experimental data.

Contribution

It introduces a novel microscopic framework combining FMD and UCOM-derived interactions to accurately compute astrophysical S-factors for key reactions.

Findings

S-factor for 3He(alpha,gamma)7Be matches experimental data well

Calculated S-factor for 3H(alpha,gamma)7Li is about 15% above data

Method successfully describes bound and scattering states in a unified approach

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(alpha,gamma)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 E1 transition matrix elements between the many-body scattering and bound states. For 3He(alpha,gamma)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(alpha,gamma)7Li reaction the calculated S-factor is about 15% above the data.