The Starobinsky model of inflation and Renormalizability

TL;DR

The paper explores how the Starobinsky inflation model can be approximated by asymptotically free quadratic gravity within a specific renormalization group regime, ensuring stability and agreement with cosmological data.

Contribution

It demonstrates the approximation of the Starobinsky model by asymptotically free quadratic gravity on a stable renormalization group trajectory.

Findings

Starobinsky model aligns with asymptotically free quadratic gravity

Stable, tachyon-free regime identified below a high UV scale

Model predictions agree with CMB measurements

Abstract

The Starobinsky model was born in a cosmological scenario where conformally coupled matter quantum field fluctuations on the vacuum drive a non trivial semiclassical energy momentum tensor quadratic in curvature. The presence of an unstable de Sitter solution of the semiclassical Einstein equations contributed to spread the idea that the early universe could have experienced an inflationary epoch. Effective "$R + R^2$" models of gravity have later gained much attention since their predictions are in very good agreement with the measurements of CMB data and tensor to scalar ratio bounds. In this paper we observe how the Starobinsky model can be well approximated by the asymptotically free quadratic gravity on a part of a renormalization group trajectory (below some high UV scale) which is free from tachyonic instabilities, if a definition of ``physical'' running is employed.