High-energy behavior of the nuclear symmetry potential in asymmetric   nuclear matter
  Using the relativistic impulse approximation with empirical NN scattering amplitude and the nuclear scalar and vector densities from the relativistic mean-field theory, we evaluate the Dirac optical potential for neutrons and protons in asymmetric nuclear matter. From the resulting Schr\"{o}% dinger-equivalent potential, the high energy behavior of the nuclear symmetry potential is studied. We find that the symmetry potential at fixed baryon density is essentially constant once the nucleon kinetic energy is greater than about 500 MeV. Moreover, for such high energy nucleon, the symmetry potential is slightly negative below a baryon density of about $% \rho =0.22$ fm$^{-3}$ and then increases almost linearly to positive values at high densities. Our results thus provide an important constraint on the energy and density dependence of nuclear symmetry potential in asymmetric nuclear matter. 
Lie-Wen Chen, Che Ming Ko, Bao-An Li