Narrow Results

The medium mass modification may lead to a squeezing effect. In the baryonic medium, the mass of D meson was expected to reduce and the in-medium masses of $D^{+}$ and $D^{-}$ may show a splitting effect, and the chemical potential of D meson may be not zero. We study the squeezing effect on the yield ratio $D^{+}∕D^{-}$ with nonzero chemical potential. Due to the in-medium mass splitting, the squeezing effect on the momentum distributions of $D^{+}$ and $D^{-}$ are different. Without the squeezing effect, the yield ratio $D^{+}∕D^{-}$ remains constant as the transverse momentum increases. The yield ratio $D^{+}∕D^{-}$ is affected by the squeezing effect, resulting in a dependence on transverse momentum. An increase in transverse momentum leads to a decrease in the yield ratio, especially when there is a high chemical potential. Additionally, the in-medium mass splitting amplifies this phenomenon. The yield ratio $D^{+}∕D^{-}$ with nonzero chemical potential approaches 1 when there is a large average in-medium mass reduction, which becomes more evident at higher transverse momentum. The study of the squeezing effect on the yield ratio $D^{+}∕D^{-}$ with nonzero chemical potential may be meaningful for the CBM and PANDA experiments of the FAIR project at GSI.

We consider chiral symmetry breaking at nonzero chemical potential and discuss the relation with the spectrum of the Dirac operator. We solve the so called Silver Blaze Problem that the chiral condensate at zero temperature does not depend on the chemical potential while this is not the case for the Dirac spectrum and the weight of the partition function.

The random matrix model approach to quantum chromodynamics (QCD) with nonvanishing chemical potential is reviewed. The general concept using global symmetries is introduced, as well as its relation to field theory, the so-called epsilon regime of chiral perturbation theory (∊χPT). Two types of matrix model results are distinguished: phenomenological applications leading to phase diagrams, and an exact limit of the QCD Dirac operator spectrum matching with ∊χPT. All known analytic results for the spectrum of complex and symplectic matrix models with chemical potential are summarised for the symmetry classes of ordinary and adjoint QCD, respectively. These include correlation functions of Dirac operator eigenvalues in the complex plane for real chemical potential, and in the real plane for imaginary isospin chemical potential. Comparisons of these predictions to recent lattice simulations are also discussed.

We study spectral properties of two-color QCD with an even number of flavors at high baryon density. We construct the low-energy effective Lagrangian for the Nambu-Goldstone bosons, derive Leutwyler-Smilga-type spectral sum rules and construct a suitable random matrix theory. Our results can in principle be tested in lattice QCD simulations.