A general theory of linear cosmological perturbations: scalar-tensor and vector-tensor theories

Journal Article · Mon Aug 01 04:00:00 EDT 2016 · Journal of Cosmology and Astroparticle Physics

DOI:https://doi.org/10.1088/1475-7516/2016/08/007· OSTI ID:22679554

Lagos, Macarena; Baker, Tessa; Ferreira, Pedro G.; Noller, Johannes ^[1]

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1. Astrophysics, University of Oxford, DWB, Keble road, Oxford, OX1 3RH U.K. (United Kingdom)

We present a method for parametrizing linear cosmological perturbations of theories of gravity, around homogeneous and isotropic backgrounds. The method is sufficiently general and systematic that it can be applied to theories with any degrees of freedom (DoFs) and arbitrary gauge symmetries. In this paper, we focus on scalar-tensor and vector-tensor theories, invariant under linear coordinate transformations. In the case of scalar-tensor theories, we use our framework to recover the simple parametrizations of linearized Horndeski and ''Beyond Horndeski'' theories, and also find higher-derivative corrections. In the case of vector-tensor theories, we first construct the most general quadratic action for perturbations that leads to second-order equations of motion, which propagates two scalar DoFs. Then we specialize to the case in which the vector field is time-like (à la Einstein-Aether gravity), where the theory only propagates one scalar DoF. As a result, we identify the complete forms of the quadratic actions for perturbations, and the number of free parameters that need to be defined, to cosmologically characterize these two broad classes of theories.

• OSTI ID: 22679554
• Journal Information: Journal of Cosmology and Astroparticle Physics, Journal Name: Journal of Cosmology and Astroparticle Physics Journal Issue: 08 Vol. 2016; ISSN 1475-7516
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CORRECTIONS
COSMOLOGICAL MODELS
DEGREES OF FREEDOM
DISTURBANCES
EQUATIONS OF MOTION
GAUGE INVARIANCE
GRAVITATION
PERTURBATION THEORY
TRANSFORMATIONS
VECTOR FIELDS