Dissipative effects in the expansion of the Universe. II. A multicomponent model for neutrino dissipation of anisotropy in the early Universe

A detailed multicomponent model is developed for dissipative processes in Euclidean homogeneous cosmological models. These processes involve neutrinos which might have long mean free times tp, in interaction with other constituents (electrons, photons) which are thermalized by electromagnetic interactions, and whose weak interactions produce thermal neutrinos with mean rate tj1. The method used is a mean-free-time approximation generalized to the different rates of destruction and production and tj1. We find that all models which begin collision dominated have effective heating and that this occurs even when the mass fraction of neutrinos is very small, K = p /p lO- . We also find that the neutrinos are replenished sufficiently to maintain their number at roughly the adiabatic value, so that heating is not stopped by the depletion of neutrinos. Finally, we point out that extremely long mean free paths (less than 0.01 collisions per radius of the Universe) can still give very effective heating. The solutions we find cannot be described by power laws in the time t, although some of the parameters of the solution can be so described.