Isospin and density waves in asymmetric nuclear matter

Abstract

The excitation of small density oscillations (zero sound) and isospin oscillations (isospin sound) in cold asymmetric nuclear matter (in the ground state ϱ 0 n > ϱ 0 p , ϱ 0 = ϱ 0 n + ϱ 0 p = 0.17 nucleons/fm 3) is investigated within the framework of the Landau theory of normal Fermi liquids. There is only one undamped mode of excitation, which consists predominantly of isospin oscillations, with some admixture of density oscillations. The phase velocity of this undamped wave depends very weakly on the neutron excess and is close to that of a pure isospin wave (isospin sound) in symmetric nuclear matter of the same density. At the neutron excess corresponding to that existing in heavy nuclei the amplitude of the density oscillations constitutes about 30 % of the amplitude of the neutron excess density oscillations. Calculation with a suitably parametrized charge dependent quasiparticle interaction in asymmetric nuclear matter shows that for ( ϱ 0 n − ϱ 0 p)/ ϱ 0 > 0.63 both zero sound and isospin sound are strongly damped.