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arXiv · 2209.02176

Generalized disformal Horndeski theories: cosmological perturbations and consistent matter coupling

Kazufumi Takahashi·Masato Minamitsuji·Hayato Motohashi
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Abstract

Invertible disformal transformations are a useful tool to investigate ghost-free scalar-tensor theories. By performing a higher-derivative generalization of the invertible disformal transformation on Horndeski theories, we construct a novel class of ghost-free scalar-tensor theories, which we dub generalized disformal Horndeski theories. Specifically, these theories lie beyond the quadratic/cubic DHOST class. We explore cosmological perturbations to identify a subclass where gravitational waves propagate at the speed of light and clarify the conditions for the absence of ghost/gradient instabilities for tensor and scalar perturbations. We also investigate the conditions under which a matter field can be consistently coupled to these theories without introducing unwanted extra degrees of freedom.

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Kazufumi Takahashi, Masato Minamitsuji, Hayato Motohashi. 2022-09-06. Generalized disformal Horndeski theories: cosmological perturbations and consistent matter coupling. https://doi.org/10.1093/ptep/ptac161

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