Intellectual merit: A central goal in nuclear physics research is to understand nuclear structure such as the atomic nucleus from the underlying theory of Quantum Chromodynamics (QCD). Without the atomic nucleus, chemical elements and life itself cannot exist.  At low-energies relevant for nuclear structure, QCD is a strongly interacting theory where direct pencil and paper calculation is not feasible. Nuclear reactions at low energy play a crucial role in the synthesis of elements that we find in the universe.  Major US investment in experiments such as those planned in the Facility for Rare Isotope Beams (FRIB) at the Michigan State University are going to explore properties of atomic nuclei that are important in element synthesis. Nuclear theory plays an important role. Often the low energies relevant for nuclear synthesis are not directly accessible in experiments. Theory is needed to extrapolate and interpret experimental data.  The theoretical method of effective field theory (EFT) can play an important role in this. EFT provides a model-independent framework to calculate nuclear properties and reactions with reliable error estimates. Further, EFT enables a direct link between measurements and calculation of nuclear properties, and the fundamental theory of QCD. 

EFT defined on a space-time lattice (lattice EFT) has been very successful in calculating masses and energy levels of atomic nuclei. The research conducted under the current NSF grant extend these calculations to the study of dynamical properties that is necessary to understand nuclear reactions at low-energy. One key technical aspect of this research is the systematic inclusion of the Coulomb repulsion between the positive charged atomic nuclei in the lattice EFT calculations, which has not been addressed in the past. 

Outcomes: The PI developed a numerical method called the adiabatic projection method for calculating reactions at low-energy. The numerical lattice method was tested and compared with known analytical results involving simple nuclear systems such as neutron and deuteron scattering, proton-proton fusion, etc.  Encouraged by these results, alpha-alpha scattering was successfully calculated for the first time from a completely microscopic theory where each alpha particle is comprised of two protons and two neutrons.  This calculation involving 8-particles (4 per alpha particle) opened the path for future calculations involving alpha capture on carbon-12 that plays an important role in the synthesis of oxygen-16, crucial for life, in the stars.  

Analytical formulation of EFT for weakly bound atomic nuclei that is complimentary to the numerical lattice method has been developed. Electromagnetic properties of weakly bound nuclei, and their reaction rates have been calculated. These exotic nuclei provide crucial information about the limit of stability of atomic nuclei.

Broader impact: The funds from the NSF grant contributed towards graduate student education and research at Mississippi State University (MSU). The graduate student training in computational science and analytical work has contributed towards strengthening the national pool of scientifically skilled workers in the U.S.  The geographic diversity of nuclear physics research in the U.S. was enhanced. Research from this proposal was used in an advanced Quantum Mechanics course at MSU, training a new generation of scientists. The proposed work introduced new methodologies for calculating nuclear reactions in weakly bound systems with reliable error estimates. This ties in well with the planned U.S. investment in rare isotope beam experiments. Dissemination of the results though website and journal publication has enhanced scientific understanding.  The field of atomic physics would also benefit from the work done in the weakly bound systems because of certain universality that weakly bound nuclear and atomic systems share. 

Last Modified: 11/25/2016
Modified by: Gautam Rupak