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Universe 2018, 4(8), 85;

The Polarizations of Gravitational Waves

School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
This paper is based on the talk on the International Conference on Quantum Gravity, Shenzhen, China, 26–28 March 2018.
Author to whom correspondence should be addressed.
Received: 25 June 2018 / Revised: 1 August 2018 / Accepted: 1 August 2018 / Published: 6 August 2018
(This article belongs to the Special Issue Gravity, Black Holes and Cosmology XXI)
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The gravitational wave provides a new method to examine General Relativity and its alternatives in the high speed, strong field regime. Alternative theories of gravity generally predict more polarizations than General Relativity, so it is important to study the polarization contents of theories of gravity to reveal the nature of gravity. In this talk, we analyze the polarization contents of Horndeski theory and f(R) gravity. We find out that in addition to the familiar plus and cross polarizations, a massless Horndeski theory predicts an extra transverse polarization, and there is a mix of pure longitudinal and transverse breathing polarizations in the massive Horndeski theory and f(R) gravity. It is possible to use pulsar timing arrays to detect the extra polarizations in these theories. We also point out that the classification of polarizations using Newman–Penrose variables cannot be applied to massive modes. It cannot be used to classify polarizations in Einstein-æther theory or generalized Tensor-Vector-Scalar (TeVeS) theory, either. View Full-Text
Keywords: gravitational waves; polarizations; E(2) classification gravitational waves; polarizations; E(2) classification

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Gong, Y.; Hou, S. The Polarizations of Gravitational Waves. Universe 2018, 4, 85.

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