PUB - Publikationen an der Universität Bielefeld

Scalar cosmological perturbations of a weakly self-interacting plasma mixed with a perfect radiation fluid are investigated. Effects of this plasma are considered through order lambda(3/2) of perturbative thermal-field theory in the radiation dominated universe. The breakdown of thermal perturbation theory at vastly subhorizon scales is circumvented by a Pade approximant solution. Compared to collisionless plasmas the phase speed and subhorizon damping of the plasma density perturbations are changed. An exampled for a self-interacting thermal field is provided by the neutrinos with effective 4-fermion interactions.