First CMB Constraints on the Inflationary Reheating Temperature

TL;DR

This paper uses WMAP7 CMB data to set the first Bayesian constraints on the inflationary reheating temperature, providing lower bounds that complement gravitino bounds and impacting inflation model viability.

Contribution

It introduces a Bayesian method to constrain the reheating epoch from CMB data, characterizing it with a reheating parameter and deriving bounds on reheating temperature for different inflation models.

Findings

Reheating temperature bounds are higher than collider energies for large field models.

Lower bounds on reheating temperature are established for small field models.

WMAP7 data constrains the inflationary potential parameters, favoring certain inflation models.

Abstract

We present the first Bayesian constraints on the single field inflationary reheating era obtained from Cosmic Microwave Background (CMB) data. After demonstrating that this epoch can be fully characterized by the so-called reheating parameter, we show that it is constrained by the seven years Wilkinson Microwave Anisotropies Probe (WMAP7) data for all large and small field models. An interesting feature of our approach is that it yields lower bounds on the reheating temperature which can be combined with the upper bounds associated with gravitinos production. For large field models, we find the energy scale of reheating to be higher than those probed at the Large Hadron Collider, Ereh > 17.3 TeV at 95% of confidence. For small field models, we obtain the two-sigma lower limits Ereh > 890 TeV for a mean equation of state during reheating <wreh> = -0.3 and Ereh > 390 GeV for <wreh> = -0.2. The physical origin of these constraints is pedagogically explained by means of the slow-roll approximation. Finally, when marginalizing over all possible reheating history, the WMAP7 data push massive inflation under pressure (p < 2.2 at 95% of confidence where p is the power index of the large field potentials) while they slightly favor super-Planckian field expectation values in the small field models.