We construct from chiral effective field theory two- and three-body forces a microscopic global nucleon-nucleus optical potential suitable for reactions involving radioactive isotopes. Within the improved local density approximation and without any adjustable parameters, we begin by computing local proton and neutron optical potentials for 1800 target nuclei in the mass range 12 < A < 242 and for energies between
0 MeV < E < 200 MeV. We then construct a global optical potential parametrization that depends smoothly on the projectile energy as well as the target nucleus mass number and isospin asymmetry. Elastic scattering observables calculated from the global optical potential are found to be in good agreement with available experimental data for a wide range of projectile energies and target nuclei. Compared to traditional phenomenological optical potentials, we find a strong energy dependence and shell structure features in the Woods-Saxon geometry parameters. For target nuclei with small proton-neutron asymmetry, we find that the real and imaginary optical potential depths exhibit a clear linear dependence on the isospin-asymmetry and preserve the well known Lane form up to high projectile energies. For nuclei with larger isospin asymmetries, we find evidence for a novel isoscalar term in the low-energy optical potential proportional to the square of the isospin asymmetry. These insights from microscopic many-body theory may be used to inform next-generation phenomenological optical potentials for proton- and neutron-rich isotopes.
We formulate microscopic neutron-nucleus optical potentials from many-body perturbation theory based on chiral two- and three-body forces. The neutron self-energy is first calculated in homogeneous matter to second order in perturbation theory, which gives the central real and imaginary terms of the optical potential. The real spin-orbit term is calculated separately from the density matrix expansion using the same chiral interaction as in the self-energy. Finally, the full neutronnucleus optical potential is derived within the improved local density approximation utilizing mean field models consistent with the chiral nuclear force employed. We compare the results of the microscopic calculations to phenomenological models and experimental data up to projectile energies of E = 200 MeV. Experimental elastic differential scattering cross sections and vector analyzing powers are generally well reproduced by the chiral optical potential, but we find that total cross sections are overestimated at high energies.
We formulate microscopic optical potentials for nucleon-nucleus scattering from chiral two- and three-nucleon forces. The real and imaginary central terms of the optical potentials are obtained from the nucleon self energy in infinite nuclear matter at a given density and isospin asymmetry, calculated self-consistently to second order in many-body perturbation theory. The real spin-orbit term is extracted from the same chiral potential using an improved density matrix expansion. The densitydependent optical potential is then folded with the nuclear density distributions of 40,42,44,48Ca from which we study proton-nucleus elastic scattering and total reaction cross sections using the reaction code TALYS. We compare the results of the microscopic calculations to those of phenomenological models and experimental data up to projectile energies of E = 180 MeV. While overall satisfactory agreement with the available experimental data is obtained, we find that the elastic scattering and total reaction cross sections can be significantly improved with a weaker imaginary optical potential, particularly for larger projectile energies.
We compute from chiral two- and three-body forces the complete quasiparticle interaction in symmetric nuclear matter up to twice nuclear matter saturation density. Second-order perturbative contributions that account for Pauli-blocking and medium polarization are included, allowing for an exploration of the full set of central and noncentral operator structures permitted by symmetries and the long-wavelength limit. At the Hartree-Fock level, the next-to-next-to-leading order threenucleon force contributes to all noncentral interactions, and their strengths grow approximately linearly with the nucleon density up that of saturated nuclear matter. Three-body forces are shown to enhance the already strong proton-neutron effective tensor interaction, while the corresponding like-particle tensor force remains small. We also find a large isovector cross-vector interaction but small center-of-mass tensor interactions in the isoscalar and isovector channels. The convergence of the expansion of the noncentral quasiparticle interaction in Landau parameters and Legendre polynomials is studied in detail.