Asymptotically free and safe quantum gravity scenarios consistent with Hubble, laboratory, and inflation scale physics

TL;DR

This paper explores quantum gravity scenarios that are consistent with cosmological and laboratory observations by numerically analyzing non-perturbative renormalization group equations, identifying trajectories towards asymptotic freedom and safety.

Contribution

It introduces a numerical investigation of quadratic gravity's renormalization group flows, revealing two possible regimes compatible with current observational constraints.

Findings

Identified trajectories leading to asymptotically free gravity.

Found trajectories flowing to asymptotically safe gravity.

Highlighted the need for additional observational data for early-universe scenarios.

Abstract

To find out the possible scenarios for quantum gravity consistent with the observed universe, we numerically investigate the non-perturbative renormalization group equations of a general quadratic gravity theory recently derived by Sen, Wetterich and Yamada (\textit{JHEP} 03 (2022) 130). As boundary conditions, we impose consistency with the Hubble scale and the laboratory scale experiments, and the Starobinsky model of inflation. We find two kinds of trajectories which go to different regime at the trans-Planckian scales: i) a trajectory which flows to the asymptotically free regime, and ii) a trajectory which flows to the asymptotically safe regime. To determine the early-time cosmological scenario, an additional observational data from beyond the homogeneous and isotropic space-time is necessary.