Information Gain on Reheating: the One Bit Milestone

TL;DR

This paper quantifies the information gained from Planck 2015 and BICEP2/KECK CMB data about the reheating phase after inflation, showing a significant 0.82-bit increase over previous constraints.

Contribution

It introduces a comprehensive method using Kullback-Leibler entropy across nearly 200 inflation models to robustly measure information gain on reheating from CMB data.

Findings

Information gain of 0.82 ± 0.13 bits on reheating.

40% improvement over Planck 2013 constraints.

Method applies Bayesian evidence-weighted averaging across models.

Abstract

We show that the Planck 2015 and BICEP2/KECK measurements of the Cosmic Microwave Background (CMB) anisotropies provide together an information gain of 0.82 +- 0.13 bits on the reheating history over all slow-roll single-field models of inflation. This corresponds to a 40% improvement compared to the Planck 2013 constraints on the reheating. Our method relies on an exhaustive CMB data analysis performed over nearly 200 models of inflation to derive the Kullback-Leibler entropy between the prior and the fully marginalized posterior of the reheating parameter. This number is a weighted average by the Bayesian evidence of each model to explain the data thereby ensuring its fairness and robustness.