Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 7, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1475-7516/2017/07/022
Keywords
cosmological perturbation theory; physics of the early universe; cosmology of theories beyond the SM
Funding
- Discovery Grant from Natural Science and Engineering Research Council of Canada
- Perimeter Institute
- Government of Canada through the Department of Innovation, Science and Economic Development Canada
- Province of Ontario through the Ministry of Research, Innovation and Science
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This paper presents the first derivation of the quadratic action for curvature perturbations, ?, within the framework of cuscuton gravity. We study the scalar cosmological perturbations sourced by a canonical single scalar field in the presence of cuscuton field. We identify ? as comoving curvature with respect to the source field and we show that it retains its conservation characteristic on super horizon scales. The result provides an explicit proof that cuscuton modification of gravity around Friedmann-Lemaitre-Robertson-Walker (FLRW) metric is ghost free. We also investigate the potential development of other instabilities in cuscuton models. We find that in a large class of these models, there is no generic instability problem. However, depending on the details of slow-roll parameters, specific models may display gradient instabilities.
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