Metric preheating and radiative decay in single-field inflation

Jérôme Martin (1) , Theodoros Papanikolaou (2) , Lucas Pinol (1) , Vincent Vennin (1, 2)

1 IAP - Institut d'Astrophysique de Paris
2 APC (UMR_7164) - AstroParticule et Cosmologie

At the end of inflation, the inflaton oscillates at the bottom of its potential and these oscillations trigger a parametric instability for scalar fluctuations with wavelength λ comprised in the instability band (3H m)−1/2 <λ < H−1, where H is the Hubble parameter and m the curvature of the potential at its minimum. This “metric preheating” instability, which proceeds in the narrow resonance regime, leads to various interesting phenomena such as early structure formation, production of gravitational waves and formation of primordial black holes. In this work we study its fate in the presence of interactions with additional degrees of freedom, in the form of perturbative decay of the inflaton into a perfect fluid. Indeed, in order to ensure a complete transition from inflation to the radiation-dominated era, metric preheating must be considered together with perturbative reheating. We find that the decay of the inflaton does not alter the instability structure until the fluid dominates the universe content. As an application, we discuss the impact of the inflaton decay on the production of primordial black holes from the instability. We stress the difference between scalar field and perfect fluid fluctuations and explain why usual results concerning the formation of primordial black holes from perfect fluid inhomogeneities cannot be used, clarifying some recent statements made in the literature.

Mots clés: physics of the early universe; inflation; primordial black holes; black hole: primordial; inflaton: decay; stability: parametric; fluctuation: scalar; field theory: scalar; preheating; structure; formation; black hole: formation; gravitational radiation; narrow resonance; Hubble constant; radiative decay; inflaton: oscillation; curvature: perturbation; reheating; cosmological model; energy: density; Klein-Gordon equation

Domaines: Astrophysique [astro-ph]; Relativité Générale et Cosmologie Quantique [gr-qc]; Physique des Hautes Energies - Théorie [hep-th]

Jérôme Martin, Theodoros Papanikolaou, Lucas Pinol, Vincent Vennin. Metric preheating and radiative decay in single-field inflation. JCAP, 2020, 05, pp.003. ⟨10.1088/1475-7516/2020/05/003⟩. ⟨hal-02491301⟩