Early universe in quantum gravity

TL;DR

This paper proposes a new model of the early universe within finite nonlocal quantum gravity that naturally resolves classical cosmological problems through Weyl invariance, without requiring inflation.

Contribution

It introduces a two-phase early universe model in Weyl-invariant quantum gravity, providing universal solutions to big bang issues without inflation.

Findings

Weyl invariance addresses singularity, flatness, and horizon problems universally.

The universe transitions from a Weyl-invariant phase to a radiation-dominated phase.

Primordial perturbations arise after spontaneous symmetry breaking in the model.

Abstract

We present a new picture of the early universe in finite nonlocal quantum gravity, which is Weyl invariant at the classical and quantum levels. The high-energy regime of the theory consists of two phases, a Weyl invariant trans-Planckian phase and a post-Planckian or Higgs phase described by an action quadratic in the Ricci tensor and where the cosmos evolves according to the standard radiation-dominated model. In the first phase, all the issues of the hot big bang such as the singularity, flatness, and horizon problems find a universal and simple non-inflationary solution by means of Weyl invariance, regardless of the microscopic details of the theory. In the second phase, once Weyl symmetry is spontaneously broken, primordial perturbations are generated around a background that asymptotically evolves as a radiation-dominated flat Friedmann--Lema\^{i}tre--Robertson--Walker universe.