B. Behera et al., CAUSAL VIOLATION OF THE SPEED OF SOUND AND THE EQUATION OF STATE OF NUCLEAR-MATTER, Journal of physics. G, Nuclear and particle physics, 23(4), 1997, pp. 445-455
The causal violation of the adiabatic speed of sound in nuclear matter
at high density and/or high temperature is studied with phenomenologi
cal density-dependent effective interactions within the framework of t
he density matrix expansion and the non-relativistic Fermigas model. T
his study shows that the causal violation is essentially governed by t
he range of the exchange component and the nature of the density depen
dence of the effective interaction used to derive the equation of stat
e (EOS) of nuclear matter as a function of density and temperature. Wi
th a model effective interaction consisting of a short-range density-d
ependent part of delta-function form and a long-range density-independ
ent part of Gaussian form, it is observed that the causal violation ca
n be completely avoided if the long-range part of the exchange compone
nt of the interaction has a range mu(ex) greater than or equal to 1.2f
and if the density dependence of the interaction is chosen in the for
m (rho/1 + c(3) rho)(g)amma with (1 + 1/c(3) rho(nm))(gamma+1) less th
an or equal to mc(2)/(T-F/5 - epsilon(nm)) instead of the Skyrme appro
ximation rho(g)amma. The implications of these restrictions on the eff
ective interaction imposed by causality are also discussed.