R. Maartens et J. Triginer, DENSITY PERTURBATIONS WITH RELATIVISTIC THERMODYNAMICS, Physical review. D. Particles and fields, 56(8), 1997, pp. 4640-4650
We investigate cosmological density perturbations in a covariant and g
auge-invariant formalism, incorporating relativistic causal thermodyna
mics to give a self-consistent description. The gradient of density in
homogeneities splits covariantly into a scalar part, equivalent to the
usual density perturbations, a rotational vector part that is determi
ned by the vorticity, and a tensor part that describes the shape. We g
ive the evolution equations for these parts in the general dissipative
case. Causal thermodynamics gives evolution equations for viscous str
ess and heat flux, which are coupled to the density perturbation equat
ion and to the entropy and temperature perturbation equations. We give
the full coupled system in the general dissipative case, and simplify
the system in certain cases. A companion paper uses the general forma
lism to analyze damping of density perturbations before last scatterin
g. [S0556-2821(97)05420-9].