Spectral functions for (D)over-bar and <(D0* )over bar> mesons in nuclear matter with partial restoration of chiral symmetry

We investigate the in-medium masses of a (D) over bar (0 ) meson and a <(D-0(*) )over bar> (0(vertical bar)) meson, and spectral functions for (D) over bar and <(D-0(*) )over bar> meson channels in nuclear matter. These mesons are introduced as chiral partners in the chiralsymmetry-broken vacuum, hence they are useful to explore the partial restoration of the broken chiral symmetry in nuclear matter. We consider the linear sigma model to describe the chiral symmetry breaking and to investigate a qualitative tendency of changes of (D) over bar mesons at low density. Our study shows that the loop corrections to (D) over bar and <(D-0(*) )over bar> meson masses provide a smaller mass splitting at finite density than that in vacuum, a result that indicates a tendency of the restoration of the chiral symmetry. We investigate also the spectral function for <(D-0(*) )over bar> meson channel, and find three peaks. The first peak, which corresponds to the resonance of the <(D-0(*) )over bar> meson, is broadened by collisions with nucleons in medium, and the peak position shifts to lower mass due to the partial restoration of chiral symmetry as the density increases. The second peak is identified as a threshold enhancement which shows a remarkable enhancement as the density increases. The third peak is Landau damping. The obtained properties of (D) over bar and <(D-0(*) )over bar> mesons in nuclear matter will provide useful information for experiments.