Nonclassical state representation of inflaton and power-law expansion in FRW universe

Abstract

We have examined a homogeneous massive scalar field minimally coupled to the spatially flat Friedmann-Robertson-Walker metric, in squeezed and coherent state formalisms, in semiclassical theory of gravity. In the oscillatory phase of inflaton, the approximate leading solution to the semiclassical Einstein equation has the same power-law expansion as that of the classical Einstein equation for both coherent and squeezed state formalisms. Quantum fluctuations of the inflaton in coherent and squeezed vacuum states are studied, by using dispersion relations. The uncertainty relation for coherent state does not depend on the coherent state parameter while the uncertainty relation for squeezed vacuum state depends on the associated squeezing parameter and squeezing angle.