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arXiv · 1406.2402

Effective field theory of modified gravity on the spherically symmetric background: leading order dynamics and the odd-type perturbations

Ryotaro Kase·László Árpád Gergely·Shinji Tsujikawa
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Abstract

We consider perturbations of a static and spherically symmetric background endowed with a metric tensor and a scalar field in the framework of the effective field theory of modified gravity. We employ the previously developed 2+1+1 canonical formalism of a double Arnowitt-Deser-Misner (ADM) decomposition of space-time, which singles out both time and radial directions. Our building block is a general gravitational action that depends on scalar quantities constructed from the 2+1+1 canonical variables and the lapse. Variation of the action up to first-order in perturbations gives rise to three independent background equations of motion, as expected from spherical symmetry. The dynamical equations of linear perturbations follow from the second-order Lagrangian after a suitable gauge fixing. We derive conditions for the avoidance of ghosts and Laplacian instabilities for the odd-type perturbations. We show that our results not only incorporates those derived in the most general scalar-tensor theories with second-order equations of motion (the Horndeski theories) but they can be applied to more generic theories beyond Horndeski.

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Ryotaro Kase, László Árpád Gergely, Shinji Tsujikawa. 2014-12-06. Effective field theory of modified gravity on the spherically symmetric background: leading order dynamics and the odd-type perturbations. https://doi.org/10.1103/physrevd.90.124019

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