title: Ab initio alpha-alpha scattering.
abstract: Processes such as the scattering of alpha particles ((4)He), the triple-alpha reaction, and alpha capture play a major role in stellar nucleosynthesis. In particular, alpha capture on carbon determines the ratio of carbon to oxygen during helium burning, and affects subsequent carbon, neon, oxygen, and silicon burning stages. It also substantially affects models of thermonuclear type Ia supernovae, owing to carbon detonation in accreting carbon-oxygen white-dwarf stars. In these reactions, the accurate calculation of the elastic scattering of alpha particles and alpha-like nuclei--nuclei with even and equal numbers of protons and neutrons--is important for understanding background and resonant scattering contributions. First-principles calculations of processes involving alpha particles and alpha-like nuclei have so far been impractical, owing to the exponential growth of the number of computational operations with the number of particles. Here we describe an ab initio calculation of alpha-alpha scattering that uses lattice Monte Carlo simulations. We use lattice effective field theory to describe the low-energy interactions of protons and neutrons, and apply a technique called the 'adiabatic projection method' to reduce the eight-body system to a two-cluster system. We take advantage of the computational efficiency and the more favourable scaling with system size of auxiliary-field Monte Carlo simulations to compute an ab initio effective Hamiltonian for the two clusters. We find promising agreement between lattice results and experimental phase shifts for s-wave and d-wave scattering. The approximately quadratic scaling of computational operations with particle number suggests that it should be possible to compute alpha scattering and capture on carbon and oxygen in the near future. The methods described here can be applied to ultracold atomic few-body systems as well as to hadronic systems using lattice quantum chromodynamics to describe the interactions of quarks and gluons.
authors.affiliation: Helmholtz-Institut für Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Universität Bonn, D-53115 Bonn, Germany.
authors.forename: Serdar
authors.initials: S
authors.lastname: Elhatisari
authors.affiliation: Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA.
authors.forename: Dean
authors.initials: D
authors.lastname: Lee
authors.affiliation: Department of Physics and Astronomy and the HPC2 Center for Computational Sciences, Mississippi State University, Mississippi State, Mississippi 39762, USA.
authors.forename: Gautam
authors.initials: G
authors.lastname: Rupak
authors.affiliation: Institut für Theoretische Physik II, Ruhr-Universität Bochum, D-44870 Bochum, Germany.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Epelbaum
authors.affiliation: Institut für Theoretische Physik II, Ruhr-Universität Bochum, D-44870 Bochum, Germany.
authors.forename: Hermann
authors.initials: H
authors.lastname: Krebs
authors.affiliation: Institute for Advanced Simulation, Institut für Kernphysik, and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Timo A
authors.initials: TA
authors.lastname: Lähde
authors.affiliation: Helmholtz-Institut für Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Universität Bonn, D-53115 Bonn, Germany.|Institute for Advanced Simulation, Institut für Kernphysik, and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Luu
authors.affiliation: Helmholtz-Institut für Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Universität Bonn, D-53115 Bonn, Germany.|Institute for Advanced Simulation, Institut für Kernphysik, and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich, Germany.|JARA-High Performance Computing, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Ulf-G
authors.initials: UG
authors.lastname: Meißner