DENSITY PERTURBATIONS WITH RELATIVISTIC THERMODYNAMICS

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].