Updated constraints on large field hybrid inflation

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Abstract

We revisit the status of hybrid inflation in the light of Planck and recent BICEP2 results, taking care of possible transient violations of the slow-roll conditions as the field passes from the large field to the vacuum dominated phase. The usual regime where observable scales exit the Hubble radius in the vacuum dominated phase predicts a blue scalar spectrum, which is ruled out. But whereas assuming slow-roll one expects this regime to be generic, by solving the exact dynamics we identify the parameter space for which the small field phase is naturally avoided due to slow-roll violations at the end of the large field phase. When the number of e-folds generated at small field is negligible, the model predictions are degenerated with those of a quadratic potential. There exists also a transitory case for which the small field phase is sufficiently long to affect importantly the observable predictions. Interestingly, in this case the spectral index and the tensor to scalar ratio agree respectively with the best fit of Planck and BICEP2. This results in a Δχ2≃5.0 in favor of hybrid inflation for Planck+BICEP2 (Δχ2≃0.9 for Planck only). The last considered regime is when the critical point at which inflation ends is located in the large field phase. It is constrained to be lower than about ten times the reduced Planck mass. The analysis has been conducted with the use of Markov-chain-Monte-Carlo Bayesian method, in a reheating consistent way, and we present the posterior probability distributions for all the model parameters.

Original languageEnglish
Article number083527
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Volume90
Issue number8
DOIs
Publication statusPublished - 27 Oct 2014

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scalars
vacuum
Markov chains
predictions
critical point
tensors
heating
radii

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title = "Updated constraints on large field hybrid inflation",
abstract = "We revisit the status of hybrid inflation in the light of Planck and recent BICEP2 results, taking care of possible transient violations of the slow-roll conditions as the field passes from the large field to the vacuum dominated phase. The usual regime where observable scales exit the Hubble radius in the vacuum dominated phase predicts a blue scalar spectrum, which is ruled out. But whereas assuming slow-roll one expects this regime to be generic, by solving the exact dynamics we identify the parameter space for which the small field phase is naturally avoided due to slow-roll violations at the end of the large field phase. When the number of e-folds generated at small field is negligible, the model predictions are degenerated with those of a quadratic potential. There exists also a transitory case for which the small field phase is sufficiently long to affect importantly the observable predictions. Interestingly, in this case the spectral index and the tensor to scalar ratio agree respectively with the best fit of Planck and BICEP2. This results in a Δχ2≃5.0 in favor of hybrid inflation for Planck+BICEP2 (Δχ2≃0.9 for Planck only). The last considered regime is when the critical point at which inflation ends is located in the large field phase. It is constrained to be lower than about ten times the reduced Planck mass. The analysis has been conducted with the use of Markov-chain-Monte-Carlo Bayesian method, in a reheating consistent way, and we present the posterior probability distributions for all the model parameters.",
author = "S{\'e}bastien Clesse and J{\'e}r{\'e}my Rekier",
year = "2014",
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