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-Lemaître-Robertson-Walker universe.
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Acknowledgments
The authors are supported by grant PID2020-118159GB-C41 funded by the Spanish Ministry of Science and Innovation MCIN/AEI/10.13039/501100011033. G.C. thanks A. De Felice and S. Kuroyanagi for useful discussions. L.M. is supported by the Basic Research Program of the Science, Technology, and Innovation Commission of Shenzhen Municipality (grant no. JCYJ20180302174206969).
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Modesto, L., Calcagni, G. Early universe in quantum gravity. J. High Energ. Phys. 2024, 194 (2024). https://doi.org/10.1007/JHEP08(2024)194
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DOI: https://doi.org/10.1007/JHEP08(2024)194