Neutron star structure and Fermi-liquid properties of nuclear matter in a relativistic hadronic field theory

Neutron star properties are computed in relativistic models that contain both hadron and quark degrees of freedom. Neutron matter is assumed to have a low-density phase described by quantum hadrodynamics (QHD) and a high-density phase described by quantum chromodynamics (QCD). Several different QHD models and approximations are employed; all use parameters that reproduce the binding energy and density of equilibrium nuclear matter. Calculated neutron star properties depend primarily on the high-density equation of state and cannot be inferred from the symmetry energy or compressibility of equilibrium nuclear matter. If interactions are neglected in the QCD phase, the density of the hadron-quark phase transition is determined by one free parameter, which is the energy/volume needed to create a bubble that confines the quarks and gluons. Observed neutron star masses do not constrain this parameter, but stable neutron stars with quark cores can exist only for a limited range of parameter values. When second-order gluon-exchange corrections are included in the QCD phase, these conclusions are unchanged, and the parameter values that lead to stable hadron-quark stars are restricted even further. The Fermi-liquid properties of nuclear matter described by a relativistic quantum field theory are examined in terms of Landau's Fermi-liquid theory. The Landau parameters are derived microscopically from the ground state energy in the relativistic Dirac-Hartree-Fock approximation and are used to describe the thermodynamic properties of the system, such as the compressibility, the symmetry energy and the first sound velocity