ar X iv : h ep - p h / 01 11 07 6 v 2 1 7 Ja n 20 02 MPI - PhT 2001 - 45 Gauged Inflation

Based on thermal equilibrium between the vacuum and its relevant excita-tions a model for cosmic inflation is presented. As far as the vacuum structure is concerned the model is entirely classical. Due to a U(1) gauged inflaton field an inflationary regime can be reached without explicitly imposing slow-roll conditions. Thereby, nontrivial euclidean BPS saturation of the inflaton effectively suppresses the gravitational coupling terms in the field equations and masquerades the gauge symmetry as a Z N +1 symmetry at the point where thermal equilibrium must break down. Solving the vacuum dynamics of the gauge field in the inflaton background in the spirit of a Born-Oppenheimer approximation, a temperature dependent cosmological constant Λ = Λ(T) is obtained. The T dependence of Λ competes with the black body radiation of the (massive) gauge field during cosmic expansion. This leads to (initial condition independent) inflation at some critical value of the inflaton amplitude. The model allows for a closed, noncollapsing universe with Planckian initial density, and hence it resolves the flatness problem. With the consistent scale of inflation M ∼ 10 13 GeV GUT monopole dilution is guaranteed. Due to the prevailing Z N +1 symmetry at the end of inflation there are no Goldstone modes. Inflation is very rapidly terminated by the Minkowskian dynamics of the inflaton field in this regime, and the bulk of Λ is converted into matter. In this process, cannibalizing domains may only exist for a period irrelevant for present day cosmology. The scenario can be thought of as one stage in a temporal sequence of effectively described, nonabelian gauge theories, each generating its own inflationary regime. Today's accelerated expansion may then have a natural explanation.