Radiative 3He(α, γ)7Be reaction in halo effective field theory

In this work we study the radiative capture of He-3 on He-4 within the halo effective field theory (EFT) framework. At leading order the capture amplitude comprises the initial state s-wave strong and Coulomb interactions summed to all orders. At the same order in the expansion, leading two-body currents contribute as well. We find delicate cancelations between the various contributions, and the two-body current contributions can be replaced by appropriately enhancing the asymptotic normalizations of the Be-7 ground and first excited state wave functions. The next-to-leading order corrections come from the s-wave shape parameter and the pure Coulomb d-wave initial state interactions. We fit the EFT parameters to available scattering data and most recent capture data. Our zero-energy astrophysical S-factor estimate, S-34 similar to 0.55 keV b, is consistent within error bars with the average in the literature.