Planck limits on non-canonical generalizations of large-field inflation models

In this paper, we consider two case examples of Dirac-Born-Infeld (DBI) generalizations of canonical large-field inflation models, characterized by a reduced sound speed, c {sub S} < 1. The reduced speed of sound lowers the tensor-scalar ratio, improving the fit of the models to the data, but inc...

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Published inJournal of cosmology and astroparticle physics Vol. 2017; no. 4; p. 6
Main Authors Stein, Nina K., Kinney, William H.
Format Journal Article
LanguageEnglish
Published United States 04.04.2017
Subjects
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BORN-INFELD THEORY
INFLATIONARY UNIVERSE
RELICT RADIATION
SATELLITES
SOUND WAVES
VELOCITY
VISIBLE RADIATION
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Summary:In this paper, we consider two case examples of Dirac-Born-Infeld (DBI) generalizations of canonical large-field inflation models, characterized by a reduced sound speed, c {sub S} < 1. The reduced speed of sound lowers the tensor-scalar ratio, improving the fit of the models to the data, but increases the equilateral-mode non-Gaussianity, f {sup equil.}{sub NL}, which the latest results from the Planck satellite constrain by a new upper bound. We examine constraints on these models in light of the most recent Planck and BICEP/Keck results, and find that they have a greatly decreased window of viability. The upper bound on f {sup equil.}{sub NL} corresponds to a lower bound on the sound speed and a corresponding lower bound on the tensor-scalar ratio of r ∼ 0.01, so that near-future Cosmic Microwave Background observations may be capable of ruling out entire classes of DBI inflation models. The result is, however, not universal: infrared-type DBI inflation models, where the speed of sound increases with time, are not subject to the bound.
ISSN:1475-7516
1475-7516
DOI:10.1088/1475-7516/2017/04/006