Collective modes and response functions of relativistic asymmetric nuclear matter.

Abstract

Response functions and collective modes for asymmetric nuclear matter (N>Z) are studied by means of a relativistic kinetic equation. Nuclear matter is described by means of a field theory of nucleons coupled to neutral, scalar (\ensuremath{\sigma}), and vector (\ensuremath{\omega}) mesons and to charged vector mesions (\ensuremath{\rho}). The contribution of the exchange terms to the nucleon-nucleon interaction is also taken into account. Because of the exchange terms, the kinetic equation presents solutions which correspond to oscillations of the spin density. Finally the effects of an excess of neutrons on the response functions and on the collective modes are investigated. It is found that a collective oscillation present in symmetric nuclear matter disappears even for a small asymmetry (\ensuremath{\sim}5%).