Abstract
According to the most popular scenario, the early Universe should have experienced an accelerated expansion phase, called Cosmological Inflation, after which the standard Big Bang Cosmology would have taken place giving rise to the radiation-dominated epoch. However, the details of the inflationary scenario are far to be completely understood. Thus, in this paper we study if possible additional (exotic) cosmological phases could delay the beginning of the standard Big Bang history and alter some theoretical predictions related to the inflationary cosmological perturbations, like, for instance, the order of magnitude of the tensor-to-scalar ratio r. A post-publication change was made to this article on 4 Jun 2020 to correct the title on the webpage.
Highlights
The evolution of the very early Universe is matter of an in-depth and long-standing debate and, to date, it is mainly the subject of speculations
Due to the expansion and the consequent cooling of the Universe, at some lower energy scales the gravitational interaction decoupled and the Universe entered an hypothetical phase where only strong, weak and electromagnetic interactions were unified1 in a single force, characterized by a single coupling constant, and, eventually, with the presence of supersymmetry. This phase is commonly known as Grand Unified epoch and it is described by a corresponding Grand Unified Theory (GUT) based, for instance, on a gauge group like SU (5) or SO(10), that contains the gauge group of the Standard Model of particle physics [1, 2, 3]
It is possible to put bounds on the reheating scale of the Universe after inflation [15], as well as to extend in a non trivial way the inflationary predictions related to the cosmological fluctuations produced during inflation, at least within certain classes of inflationary models [14, 15]
Summary
The evolution of the very early Universe is matter of an in-depth and long-standing debate and, to date, it is mainly the subject of speculations. 2. The Universe’s history before the Big Bang Nucleosynthesis The evolution of the Universe after the hypothetical inflationary/reheating era represents a further conundrum, because the underlying physics is not under control being the energy scale typically above the TeV scale at which the Electroweak (EW) and the Quantum Chromodynamics (QCD) phase transitions take place. The Universe’s history before the Big Bang Nucleosynthesis The evolution of the Universe after the hypothetical inflationary/reheating era represents a further conundrum, because the underlying physics is not under control being the energy scale typically above the TeV scale at which the Electroweak (EW) and the Quantum Chromodynamics (QCD) phase transitions take place In this framework, an early post-inflationary radiation dominated Universe would be the expected standard scenario but not the unique viable possibility. This quantity will be of crucial importance for the subsequent analysis
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