Structure of Nuclei in a Relativistic Meson-Baryon Quantum Field Theory.

Relativistic Hartree equations for spherical nuclei are derived from a relativistic nuclear quantum field theory using a coordinate-space Green's function approach. The renormalizable field theory lagrangian includes the interaction of nucleons with (sigma), (omega), (rho), and (pi) mesons and the photon. The Hartree equations represent the "mean -field" approximation for a finite nuclear system. Coupling constants and the (sigma) meson mass are determined from the properties of nuclear matter and the rms charge radius in ('40)Ca. Calculated charge densities, neutron densities, rms radii, and single-nucleon energy levels throughout the periodic table are compared with data and with results of nonrelativistic calculations. Relativistic Hartree results agree with experiment at a level comparable to that of the most sophisticated nonrelativistic calculations to date. It is shown that the Lorentz covariance of the relativistic formalism leads naturally to density-dependent interactions between nucleons. Furthermore, nonrelativistic reduction reveals noncentral and nonlocal aspects inherent in the Hartree formalism. The success of this simple relativistic Hartree approach is attributed to these features of the interaction. Giant Resonances in a Relativistic Field Theory. Isovector giant resonances are modeled as collective excitations of a relativistic baryon-meson field theory. Eigenvalue equations for small amplitude isovector motion about the static mean-field solutions are derived. Energy spectra, transition densities, and form factors for inelastic electron scattering are calculated. Hartree-Fock Description of Nuclear Matter. Relativistic Hartree-Fock equations are solved for an infinite system of nucleons and mesons. At high densities there exists a phase transition from a Fermi "sphere" to a Fermi "shell," characterized by a discontinuity in the heat capacity. The precise value of the critical density is sensitive to the approximations. The Pion Nucleon Interaction. Relativistic Hartree -Fock equations for nucelar matter are solved for both pseudoscalar and pseudovector pion-nucleon couplings. Results are very sensitive to the form of the interaction due to the relativistic nature of the self-consistent baryon spectrum. Pseudoscalar models yield unrealistic results for normal nuclear matter in this approximation.