Bayes' Theorem, Inflation, and the Ekpyrotic Universe

TL;DR

This paper evaluates Ekpyrotic universe models against Higgs inflation using Bayesian evidence and Planck 2018 data, finding that inflation models are generally favored over Ekpyrotic scenarios.

Contribution

It introduces a systematic Bayesian comparison of Ekpyrotic and inflation models using observational data and numerical likelihood calculations.

Findings

Ekpyrotic models are less favored than Higgs inflation.

A specific Ekpyrotic model shows some preference over other Ekpyrotic models.

Bayesian evidence provides a quantitative measure for model comparison.

Abstract

We calculate the Bayesian evidences for a class of Ekpyrotic universe models, and compare with a model of single field inflation with a Higgs-type potential. Combining parsimony and observational constraints, this gives us a systematic way to evaluate the degree to which Ekpyrotic models are constrained by CMB data from Planck. We integrate the equations of motion numerically to define a likelihood using Planck 2018 data and sample this likelihood to obtain Bayesian evidences. Priors are justified and used to put Ekpyrotic models and inflation on equal footing. We find reasonable preference for one of the considered Ekpyrotic models over the others, but that even this one is disfavored compared with Higgs inflation.