Screening effects in Relativistic Models of Dense Matter at Finite Temperature

We investigate screening effects of the medium on the potential interaction between two static 'charges' for different models of dense plasmas in the one-boson exchange approximation. The potential can exhibit an oscillatory behavior, which is related to the analytic structure of the corresponding boson propagators in the complex $q$-plane. We have first revisited the one-pion exchange in a nuclear medium. In addition to Friedel oscillations, which are associated to branch cuts in the $q$-plane, there appears another oscillatory component, which arises from a pole on the pion propagator. This pole is located appart from the axes, giving rise to an oscillating Yukawa-like potential. Therefore, we call this phenomenon 'Yukawa oscillations'. This phenomenon does not appear in the Debye component of the QED screened potential, even if the coupling constant is artificially increased. We have also studied a model of QCD quark-gluon plasma. In this case, the one-gluon propagator also shows this kind of poles. At high densities and/or temperatures, where one expects perturbative QCD to be valid, the pole shifts towards large momenta.