Relativistic hydrodynamic cosmological perturbations

Relativistic cosmological perturbation analyses can be made based on severa l different fundamental gauge conditions. In the pressureless limit the var iables in certain gauge conditions show the correct Newtonian behaviors. Co nsidering the general curvature (K) and the cosmological constant (Lambda) in the background medium, the perturbed density in the comoving gauge, and the perturbed velocity and the perturbed potential in the zero-shear gauge show the same behavior as the Newtonian ones in general scales. In the firs t part, we elaborate these Newtonian correspondences. In the second part, u sing the identified gauge-invariant variables with correct Newtonian corres pondences, we present the relativistic results with general pressures in th e background and perturbation. We present the general super-sound-horizon s cale solutions of the above mentioned variables valid for general K, Lambda , smd generally evolving equation of state. We show that, for vanishing K, the super-sound-horizon scale evolution is characterised by a conserved var iable which is the perturbed three-space curvature in the comoving gauge. W e also present equations for the multi-component hydrodynamic situation and for the rotation and gravitational wave.