arXiv subjects
Publications and source records attributed to H. Nachbagauer.
The low-momentum structure of the gravitational polarization tensor of an ultrarelativistic plasma of scalar particles with $λϕ^4$ interactions is evaluated in a two-loop calculation up to and including order $λ^{3/2}$. This turns out to require an improved perturbation theory which resums a local thermal mass term as well as nonlocal hard-thermal-loop vertices of scalar and gravitational fields.
The exact solutions for linear cosmological perturbations which have been obtained for collisionless relativistic matter within thermal field theory are extended to a self-interacting case. The two-loop contributions of scalar $λϕ^4$ theory to the thermal graviton self-energy are evaluated, which give the $O(λ)$ corrections in the perturbation equations. The changes are found to be perturbative on scales comparable to or larger than the Hubble horizon, but the determination of the large-time damping behavior of subhorizon perturbations requires a resummation of thermally induced masses.