Early universe in quantum gravity
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\itre--Robertson--Walker universe.