Nuclear Structure and Reactions from Effective Field Theory

Mississippi State University, Mississippi State MS

Investigators

Abstract

Fundamental research in nuclear physics is the study of atomic nuclei. The list of all known nuclei, most of them short-lived, is in the thousands. The short-lived and exotic nuclei play an important role in the synthesis of the stable elements during Big Bang Nucleosynthesis and stellar evolution. Exotic nuclei also play an important role in element synthesis in supernova remnant sites. The temperatures and densities at which the reactions responsible for element synthesis occur are often difficult to access in terrestrial laboratories. Theory calculations play an important role in these studies. The effective field theory (EFT) formalism is applied to calculate the properties of halo nuclei. These are exotic nuclei that have excess protons or neutrons that form a halo around a core. EFT enables systematic first-principles calculations that provide rigorous uncertainty estimates that are necessary in many astrophysical models of element synthesis. Properties of asymmetric nuclear matter are also calculated using a numerical method called lattice EFT. These are important in the study of gravitational waves from colliding neutron stars and blackholes. Broader impacts of the research include training of graduate students in numerical and analytical work for an academic or industry career benefiting society. This project builds on past work by the principal investigator (PI) on halo nuclei and lattice EFT that were partly funded by previous U.S. National Science Foundation grants. Halo nuclei are abundant on the nuclear chart near the edge of stability. EFT relies on the separation of energy scales in physical systems to construct a systematic expansion for low-energy approximations. The small separation energy of the valence nucleons in halo systems is ideal for this. Multi-channel reactions in a coupled-channel formalism in the presence of strong Coulomb forces are studied. Charge radii of lithium-8 and boron-8, reactions involving triton and helium-3 with valence nucleons are considered. Bayesian analysis is used to provide uncertainty estimates and develop a robust reaction theory. Properties of asymmetric nuclear matter under conditions relevant to neutron star densities and temperatures are studied using lattice EFT. The Pinhole algorithm developed in earlier work by the PI is used in these studies. The numerical lattice method allows us to perform Monte Carlo calculations involving tens of protons and neutrons using interactions derived in EFT. The research in this project ties in with major U.S. investment 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.