Gravitational production of matter and radiation during reheating after inflation
- Authors
- Publication Date
- Sep 03, 2024
- Source
- HAL
- Keywords
- Language
- English
- License
- Unknown
- External links
Abstract
Inflation is currently the most promising theory for depicting the initial conditions in the early Universe. In the simplest models, a scalar field, the inflaton, is slowly rolling down its potential with high energy density, making the Universe exponentially expand. On top of this mechanism of accelerated expansion, quantum fluctuations of the inflaton generated on small scales can be further amplified by gravitational effects and stretched to large-scale cosmological perturbations with a near-scale invariant power spectrum. These predictions of inflationary models are in extremely good agreement with the observation of the Cosmic Microwave Background (CMB) anisotropies and Large Scale Structures (LSS). For an inflationary model to be successful, it also needs to include a viable mechanism to transfer energy from the inflaton to the other fields, producing particles of the Standard Model (SM). We call this mechanism post-inflationary reheating. Reheating can also produce Dark Matter (DM) particles, a necessary ingredient of the standard cosmological model, and to explain the dynamics of galaxies and galaxy clusters. The SM particles produced after inflation must have formed a hot primordial plasma, as highlighted by observational data on the Big Bang Nucleosynthesis (BBN) and CMB measurements. In the standard scenario, the inflaton field falls towards the potential minimum at the end of inflation, ending the accelerated expansion and oscillating around this minimum. It can then dissipate its energy while oscillating and convert it into particles through its coupling to other fields. This mechanism is crucial to understanding the evolution of the early Universe before BBN. This thesis explores the phenomenology of reheating through perturbative decays or scatterings of the inflaton towards particles of different spins. We are also interested in the effect of the equation of state during reheating and its implications on the reheating process. We especially study a mixed potential of the inflaton leading to a transition of the equation of states during reheating, and show that it can significantly alter the predictions of reheating temperature and fragmentation of the inflaton background. The main part of this thesis has been focusing on the production of particles during inflaton oscillations, mediated by Planck-suppressed gravitational interactions. We first consider the graviton portals emerging from an effective description of Einstein's gravity and generalize these results to non-minimal couplings to gravity. This framework is applied to the production of heavy DM particles of different spins as well as the production of relativistic particles of the SM. We show that the right relic abundance of DM could be easily produced through these gravitational portals and that such unavoidable gravitational effects may highly impact the early radiation production from the inflaton. Then, important implications of steep potential associated with a stiff equation of state are explored in the context of gravitational reheating, leading to an interesting signal in the primordial gravitational waves spectrum generated during inflation. This represents a signature of such a scenario and can be probed by future gravitational waves experiments, shedding light on the equation of state and temperature reached during reheating. We finally propose a minimal scenario in which both the DM relic abundance and the asymmetry between baryons and anti-baryons, are generated by gravitational portals during reheating. We rely on the framework of non-thermal leptogenesis involving a Beyond Standard Model scenario with additional heavy right-handed neutrinos. We investigate such a minimal reheating scenario to produce the right relics simultaneously during gravitational reheating, and find constraints on right-handed neutrino masses in this case.
