Relativistic Love-Franey model: Covariant representation of the NN interaction for N-nucleus scattering

A Lorentz invariant form of the NN amplitude is fit with a simple model which includes direct and exchange first Born terms from a number of mesons. The (complex) couplings and nucleon-meson form factors are adjusted to fit the NN amplitudes directly without iteration. The resulting parameters agree well with one-boson-exchange potentials and have a systematic and small energy dependence. Detailed analytic representations of the relativistic NN amplitudes are provided at lab energies of 135, 200, and 400 MeV. The model separation of the NN amplitudes into direct and exchange contributions does not involve sensitive cancellations and is contrasted with the very different nonrelativistic results. The model amplitudes are used to construct optical potentials in a relativistic impulse approximation using both pseudovector and pseudoscalar-N coupling. The pseudoscalar result reproduces earlier relativistic impulse approximation calculations which diverge at low energies, while the pseudovector results are nearly constant with energy and in good agreement with phenomenological potentials.