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arXiv · 2110.03194

Nonlinear definition of the shadowy mode in higher-order scalar-tensor theories

Antonio De Felice·Shinji Mukohyama·Kazufumi Takahashi
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Abstract

We study U-DHOST theories, i.e., higher-order scalar-tensor theories which are degenerate only in the unitary gauge and yield an apparently unstable extra mode in a generic coordinate system. We show that the extra mode satisfies a three-dimensional elliptic differential equation on a spacelike hypersurface, and hence it does not propagate. We clarify how to treat this "shadowy" mode at both the linear and the nonlinear levels.

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Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi. 2021-10-07. Nonlinear definition of the shadowy mode in higher-order scalar-tensor theories. https://doi.org/10.1088/1475-7516%2F2021%2F12%2F020

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