Asymmetric nuclear matter studied by time-dependent local isospin density approximation

Abstract

The dynamic response of asymmetric nuclear matter is studied by means of a time-dependent local isospin density approximation (TDLIDA) approach. Calculations are based on a local density energy functional derived by an auxiliary field diffusion Monte Carlo (AFDMC) calculation of bulk nuclear matter. Three types of excited states emerge: collective states, a continuum of quasiparticle-quasihole excitations and unstable solutions. These states are analyzed and discussed for different values of the nuclear density $\ensuremath{\rho}$ and isospin asymmetry $\ensuremath{\xi}=(N\ensuremath{-}Z)/A$. An analytical expression of the compressibility as a function of $\ensuremath{\rho}$ and $\ensuremath{\xi}$ is derived which shows explicitly an instability of the neutron matter around $\ensuremath{\rho}\ensuremath{\simeq}0.09$ fm${}^{\ensuremath{-}3}$ when a small fraction of protons are added to the system.