Flat limit of the de Sitter QFT in the rest frame vacuum

Abstract

The problem of the flat limits of the scalar and spinor fields on the de Sitter expanding universe is considered in the rest frame vacuum where the frequencies are separated in rest frames as in special relativity. The phases of the fundamental solutions of these fields are regularized in order to obtain Minkowskian flat limits. New expressions of scalar mode functions or Dirac spinors reaching natural flat limits are given in the rest frame vacuum and suitable approximate formulas are proposed. In this manner the flat limit is correctly defined for the entire quantum theory since the one-particle operators tend to those of special relativity.