Asymptotically Safe gravity and non-singular inflationary Big Bang with vacuum birth

TL;DR

This paper develops a model of the early universe based on asymptotically safe gravity, proposing a non-singular vacuum birth era that transitions smoothly into standard cosmology, with mechanisms for entropy production and matter inclusion.

Contribution

It introduces a novel framework combining asymptotic safety and vacuum birth to describe a non-singular early universe with entropy generation and matter evolution.

Findings

Derivation of non-singular vacuum birth solutions

Natural exit from inflation to decelerating cosmology

Mechanisms for entropy production and reheating

Abstract

General non-singular accelerating cosmological solutions for an initial cosmic period of pure vacuum birth era are derived. This vacuum era is described by a varying cosmological "constant" suggested by the Renormalisation Group flow of Asymptotic Safety scenario near the ultraviolet fixed point. In this scenario, natural exit from inflation to the standard decelerating cosmology occurs when the energy scale lowers and the cosmological "constant" becomes insignificant. In the following period where matter is also present, cosmological solutions with characteristics similar to the vacuum case are generated. Remarkably the set of equations allow for particle production and entropy generation. Alternatively, in the case of non-zero bulk viscosity, entropy production and reheating is found. As for the equations of motion, they modify Einstein equations by adding covariant kinetic terms of the cosmological "constant" which respect the Bianchi identities. An advance of the proposed framework is that it ensures a consistent description of both a quantum vacuum birth of the universe and a subsequent cosmic era in the presence of matter.