Kinetics of small perturbations in the isotropic Universe

Long-wave gravitational perturbations are considered in the isotropic expanding Universe filled by an ultrarelativistic gas . The kinetic approach in the collisionless approximation has led to a conclusion that the scalar and vector perturbations arising at the moment of νsub(o) < < 1/n (n is the wave vector, ν is time coordinate x4) increase, if at this moment the macroscopic - momentum density perturbation of the gas is nonzero. Such increase lasts until ν1=2.7νsub(o), when the macroscopic momentum density perturbation of the gas becomes zero, Also a solution for tensor perturbations in the nν < < 1 limit has been obtained