Preheating the universe in hybrid inflation

TL;DR

This paper analyzes preheating after inflation in hybrid inflation models, contrasting it with chaotic inflation. It demonstrates that end-of-inflation symmetry breaking in hybrid scenarios can support very efficient, long-lived narrow resonances, producing large occupation numbers and significant non-equilibrium dynamics across multiple fields. The discussion maps out parameter regimes defined by g^2 relative to λ, showing how coupled-field dynamics can alter instability structures beyond simple Mathieu behavior and lead to diverse resonance outcomes. It also explores observable consequences, notably a stochastic gravitational-wave background potentially detectable by LIGO in certain low-scale hybrid models, while acknowledging the challenges in predicting the final reheating temperature due to backreaction and thermalization processes.

Abstract

One of the fundamental problems of modern cosmology is to explain the origin of all the matter and radiation in the Universe today. The inflationary model predicts that the oscillations of the scalar field at the end of inflation will convert the coherent energy density of the inflaton into a large number of particles, responsible for the present entropy of the Universe. The transition from the inflationary era to the radiation era was originally called reheating, and we now understand that it may consist of three different stages: preheating, in which the homogeneous inflaton field decays coherently into bosonic waves (scalars and/or vectors) with large occupation numbers; backreaction and rescattering, in which different energy bands get mixed; and finally decoherence and thermalization, in which those waves break up into particles that thermalize and acquire a black body spectrum at a certain temperature. These three stages are non-perturbative, non-linear and out of equilibrium, and we are just beginning to understand them. In this talk I will concentrate on the preheating part, putting emphasis on the differences between preheating in chaotic and in hybrid inflation.