Nuclear Properties Using Continuum and Lattice Effective Field Theories

Mississippi State University, Mississippi State MS

Investigators

Abstract

The relative abundances of atomic nuclei, and thus the elements found in nature, require production mechanisms in extreme environments, such as those present during the Big Bang in the early universe and inside stars. One cannot create such conditions in laboratories. However, using theoretical methods, one can extrapolate terrestrial measurements to astrophysically-relevant densities and temperatures. The list of atomic nuclei, many of them short-lived, is in the thousands and nuclear theory plays a crucial role in analyzing the properties of known nuclei from measurements. In this broader picture, this project develops and applies the effective field theory (EFT) formalism to calculate several reaction rates central to the understanding of the stars' evolution, including our Sun. Key reactions for understanding the abundances of life-giving oxygen and carbon in stellar synthesis will be studied. Solar reactions that help probe physics beyond the Standard Model of particle physics will also be calculated with high precision. In addition, lattice EFT method for exact numerical calculations will be developed. The broader impacts of this research include training graduate students in nuclear physics, as well as in numerical and analytical work, for an academic or industry career that benefits society. This project builds on past work by the PI and his collaborators on halo nuclei and lattice EFT. Halo nuclei have excess protons or neutrons that form a halo around a core. The small separation energy of the valence nucleons is used as a systematic expansion parameter in the calculation. Alpha burning on carbon-12 in massive stars determines the carbon-12 to oxygen-16 ratio. Currently there is an order-of-magnitude uncertainty in the reaction rate estimates and the EFT calculation will be used for a model-independent reaction rate estimate. Alpha capture on helium is crucial for boron-8 production through a subsequent proton capture in the Sun. The energetic subatomic neutrinos from the decay of boron-8 probes physics beyond the Standard Model. The PI and his collaborators will address the discrepancy between current measurements and theoretical calculations of the radiation angular distribution emitted in this reaction. Lattice EFT is the formulation of the theory on a space-time lattice, and it allows for exact numerical calculations without resorting to a perturbative expansion. A coupled-channel calculation of helium-3 and neutron converting into triton and proton is performed using lattice EFT. The reverse reaction controls helium-3 production in Big Bang Nucleosynthesis. The research in this project aligns with major U.S. investments in rare isotope beam experiments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.