Melting of heavy vector mesons and quasinormal modes in a finite density plasma from holography

Abstract

In this work, we investigate, for the first time, the melting of charmonium states within a holographic QCD model in the context of Einstein-Maxwell-dilaton theory. In the dual field theory, the model describes the heavy mesons inside a finite temperature and density medium. First, we calculate the spectrum at zero temperature. Then, at finite temperature, we obtain the spectral functions, where the heavy vector meson are represented by peaks. We show that the charmonium melts down at temperatures above the confinement/deconfinement temperature of the quark-gluon plasma. We also observe that the chemical potential speeds up the melting process. In the gravitational side of the theory, we solve the perturbation equations in the hydrodynamic limit. From this result, we read off the diffusion coefficient, then the quark number susceptibility. We show that the quark number susceptibility computed in this way does not blow up at the critical end point. We interpret this result as the lack of backreaction on the background by the action describing the vector mesons. To get the quasinormal frequencies, we solve the perturbation equations numerically. We report the emergence of a new mode whose real part increases rapidly at a certain value of the chemical potential, while its imaginary part decreases with the increasing of the chemical potential. Finally, by comparing against results obtained in the conformal plasma, we observe that the real part of the frequency increases, while the imaginary part decreases when we consider the nonconformal plasma.