Screening Effects in Relativistic Models of Dense Matter at Finite Temperature

We investigate screening effects of the medium on the potential interactionbetween two static 'charges' for different models of dense plasmas in theone-boson exchange approximation. The potential can exhibit an oscillatorybehavior, which is related to the analytic structure of the corresponding bosonpropagators in the complex $q$-plane. We have first revisited the one-pionexchange in a nuclear medium. In addition to Friedel oscillations, which areassociated to branch cuts in the $q$-plane, there appears another oscillatorycomponent, which arises from a pole on the pion propagator. This pole islocated appart from the axes, giving rise to an oscillating Yukawa-likepotential. Therefore, we call this phenomenon 'Yukawa oscillations'. Thisphenomenon does not appear in the Debye component of the QED screenedpotential, even if the coupling constant is artificially increased. We havealso studied a model of QCD quark-gluon plasma. In this case, the one-gluonpropagator also shows this kind of poles. At high densities and/ortemperatures, where one expects perturbative QCD to be valid, the pole shiftstowards large momenta.Comment: Revtex. 9 pages, 9 figure