  Spectral functions of the pseudoscalar $D$ meson in the nuclear medium are
analyzed using QCD sum rules and the maximum entropy method. This approach
enables us to extract the spectral functions without any phenomenological
assumption, and thus to visualize in-medium modification of the spectral
functions directly. It is found that the reduction of the chiral condensates of
dimension 3 and 5 causes the masses of both $D^+$ and $D^-$ mesons to grow
gradually at finite density. Additionally, we construct
charge-conjugate-projected sum rules and find a $D^+$-$D^-$ mass splitting of
about -15 MeV at nuclear saturation density.

High Energy Physics - Phenomenology;Nuclear Theory