Reheating predictions in single field inflation

TL;DR

This paper explores how the reheating phase after inflation influences observable cosmological parameters, providing a method to constrain inflation models by linking reheating characteristics to CMB data.

Contribution

It introduces a simplified model relating reheating parameters to inflationary observables, helping to distinguish between different single-field inflation models.

Findings

Reheating duration and temperature can be constrained by CMB data.

A constant equation of state approximation links reheating to spectral index and tensor-to-scalar ratio.

Constraints help differentiate inflation models with similar predictions.

Abstract

Reheating is a transition era after the end of inflation, during which the inflaton is converted into the particles that populate the Universe at later times. No direct cosmological observables are normally traceable to this period of reheating. Indirect bounds can however be derived. One possibility is to consider cosmological evolution for observable CMB scales from the time of Hubble crossing to the present time. Depending upon the model, the duration and final temperature after reheating, as well as its equation of state, may be directly linked to inflationary observables. For single-field inflationary models, if we approximate reheating by a constant equation of state, one can derive relations between the reheating duration (or final temperature), its equation of state parameter, and the scalar power spectrum amplitude and spectral index. While this is a simple approximation, by restricting the equation of state to lie within a broad physically allowed range, one can in turn bracket an allowed range of $n_s$ and $r$ for these models. The added constraints can help break degeneracies between inflation models that otherwise overlap in their predictions for $n_s$ and $r$.