Fate of charmed mesons near chiral symmetry restoration in hot matter

Chiral thermodynamics of charmed mesons is formulated at finite temperature within a $2+1+1$-flavored effective Lagrangian incorporating heavy quark symmetry. The charmed-meson mean fields act as an extra source which breaks the chiral symmetry explicitly. This leads to effective interactions between the light and heavy-light mesons, which intrinsically depend on temperature. Effective masses of the scalar and pseudoscalar charmed-mesons tend to approach each other as increasing temperature, so that the splitting between the chiral partners is reduced. These chiral splittings are shown to be less sensitive to the light-quark flavors, attributed to the underlying heavy quark symmetry. Consequently, chiral symmetry restoration is more manifest for the strange charmed-mesons than for the strange light mesons. The effective masses are also compared with the results in the one-loop chiral perturbation theory. A substantial difference is found at a relatively low temperature, $T \sim f_\pi$.