Renormalization group improved cosmology in the presence of a stiff matter era

TL;DR

This paper investigates how renormalization group improved quantum gravity modifies early universe cosmology, showing the absence of inflation during stiff matter, but allowing inflation after the Planck time due to quantum effects.

Contribution

It introduces a renormalization group framework into cosmology with a stiff matter era, revealing quantum gravitational effects can induce inflation after the Planck time.

Findings

Inflation is absent during the stiff matter era when quantum effects are considered.

Quantum gravitational effects can trigger inflation after the Planck time.

The universe's evolution includes a matter-dominated era with accelerated expansion due to dark energy.

Abstract

In \href{https://link.aps.org/doi/10.1103/PhysRevD.92.103004}{Phys. Rev. D 92 (2015) 103004}, simple analytical solutions of the Friedman equations were obtained for a universe having stiff matter component in the early universe together with a dark matter, and a dark energy component. In this analysis, the universe is considered to be made of a dark fluid which behaves as a stiff matter in the early phase of the universe (when the internal energy dominates). It is also more logical to consider quantum gravitational effects in the early phase of the cosmological evolution. In this analysis, following \href{https://link.aps.org/doi/10.1103/PhysRevD.65.043508}{Phys. Rev. D 65 (2002) 043508}, we consider renormalization group improved modified Friedmann equations where the Newton's gravitational constant (G) and the cosmological constant (\Lambda) flows with the momentum scale of the universe. It is observed that for a universe undergoing a stiff matter era, radiation era, and matter era, inflation is absent in the early time regime of the universe when the flow of the Newton's gravitational constant and cosmological constant is under consideration. Using the identification of the momentum scale with the scale factor of the universe, we then explore the era $t>t_{\text{Pl}}$ which indicates a primarily matter dominated era with accelerated expansion due to the presence of dark energy. Finally, considering the total equation of state as a combination of linear equation of state along with a polytropic equation of state, we observe that after the Planck-time the universe can undergo an inflationary phase and we find out that the inflation is enhanced by quantum gravitational effects arising due to the consideration of renormalization group approach to quantum gravity