Decelerating and accelerating back-reaction of vacuum to the Universe expansion

TL;DR

This paper investigates how vacuum back-reaction influences the Universe's expansion, showing it can either slow down or accelerate expansion depending on the acceleration state, using a novel renormalization approach.

Contribution

It introduces an automatic renormalization method based on equations of motion to analyze vacuum back-reaction without the cosmological constant problem.

Findings

Vacuum tends to decelerate Universe expansion when conformal acceleration is zero.

Vacuum acts as a cosmological constant during accelerated expansion.

Estimates for the third derivative of the scale factor are provided.

Abstract

Back-reaction of the massless scalar field vacuum to the Universe expansion is considered. Automatic renormalization procedure based on the equations of motion instead of the Friedman equation is used to avoid the cosmological constant problem. It is found, that the vacuum tends to decelerate an expansion of Universe if the conformal acceleration of Universe is equal to zero. In contract, the vacuum acts as the true cosmological constant in Universe expanding with the present day acceleration. Estimation for third derivative of the Universe scale factor with respect to conformal time is presented.