Open-Charm Vector Mesons in Hot and Dense Nuclear Matter
We investigate the in-medium properties of the open-charm vector mesons $D_s^{*}$ and $D^{*}$ in hot and dense nuclear matter within the framework of finite-temperature and finite-density QCD sum rules. The analysis incorporates temperature- and density-dependent quark and gluon condensates together with an in-medium continuum threshold constrained by the light-quark condensate. By solving the resulting QCD sum rules, we determine the in-medium masses and leptonic decay constants of the $D_s^{*\pm}$ and $D^{*\pm}$ mesons over a broad region of the $(T,\rho)$ plane. Both vector mesons undergo substantial in-medium softening, with their masses and leptonic decay constants decreasing as the baryon density increases. The masses exhibit a non-monotonic dependence on baryon density, whereas the leptonic decay constants decrease monotonically throughout the investigated density range. Increasing temperature generally weakens the density-induced modifications, although baryon density remains the dominant driver of the in-medium evolution. The largest mass shifts occur at intermediate-to-high densities, reaching approximately $-413~\mathrm{MeV}$ for the $D_s^{*-}$ meson and $-207~\mathrm{MeV}$ for the $D^{*-}$ meson, while the leptonic decay constants are reduced by more than $68\%$ in both channels at the highest densities considered. We further investigate the particle--antiparticle splittings of the masses and leptonic decay constants induced by finite baryon density. Finite baryon density lifts the vacuum degeneracy between the charge-conjugate states, while increasing temperature generally suppresses the resulting asymmetries. Although the strange and non-strange channels exhibit similar qualitative behavior, quantitative differences emerge in both the in-medium modifications and the particle--antiparticle splittings. ....