A solution to the IR divergence problem of interacting inflaton field.

In the direct computation of the fluctuations generated during inflation, we will easily find the logarithmic divergence in the infrared(IR) limit. We focus on the fact that the usual amplitude of the fluctuation is influenced by what we cannot observe in two diffrent ways; One is due to the limitation of our observable region and the other is due to the quantum decoherence which picks up a unique history of the univers from many contained in the natural quantum state in the early stage of the universe. By removing these influences, we introduce new quantities which mimic what we really observe. We just give the outline of the proof to show that IR corrections to such quantities are actually free from divergence. [ABSTRACT FROM AUTHOR]