Off-mass-shell behaviors of nucleon self-energies and the Gamow-Teller sum rule in the relativistic hartree-fock approach

The relativistic Hartree approximation predicts a deep attractive potential for antinucleon, which largely reduces the threshold energies of the nucleon-antinucleon (NN-bar) production. This effect has played an important role in explaining the quenching of the Gamow-Teller (GT) strength because the quenched strength in the particle-hole excitation is partially taken by the NN-bar production. On the other hand antiproton experiments do not reveal a deep attractive potential for antinucleon. In this paper, we study the energy dependence of the nucleon self-energies in the relativistic Hartree-Fock (RHF) approximation in off-mass-shell states. Then, we demonstrate that the antinucleon appearing in low-energy observables is in the off-mass-shell energy region and its properties are quite different from those at the on-mass-shell state. Furthermore, we show that the quenched amount of the GT strength is taken by not only the NN-bar production but also the meson production through the imaginary part of the nucleon self-energy in the RHF approximation. (author)