TY - JOUR

T1 - Inspiral gravitational waveforms from compact binary systems in Horndeski gravity

AU - Higashino, Yurika

AU - Tsujikawa, Shinji

N1 - Funding Information:
We are grateful to Luca Amendola, Rampei Kimura, Kei-ichi Maeda, Masato Minamitsuji, Atsushi Nishizawa, Hirotada Okawa, Hiroki Takeda, David Trestini, and Nicolas Yunes for useful discussions and comments. We also thank Tan Liu for answering questions to the paper . S. T. was supported by the Grant-in-Aid for Scientific Research Fund of the JSPS No. 19K03854 and No. 22K03642.
Publisher Copyright:
© 2023 American Physical Society.

PY - 2023/2/15

Y1 - 2023/2/15

N2 - In a subclass of Horndeski theories with the speed of gravity equivalent to that of light, we study gravitational radiation emitted during the inspiral phase of compact binary systems. We compute the waveform of scalar perturbations under a post-Newtonian expansion of energy-momentum tensors of pointlike particles that depend on a scalar field. This scalar mode not only gives rise to breathing and longitudinal polarizations of gravitational waves, but it is also responsible for scalar gravitational radiation in addition to energy loss associated with transverse and traceless tensor polarizations. We calculate the Fourier-transformed gravitational waveform of two tensor polarizations under a stationary phase approximation and show that the resulting waveform reduces to the one in a parametrized post-Einsteinian (ppE) formalism. The ppE parameters are directly related to a scalar charge in the Einstein frame, whose existence is crucial to allow the deviation from general relativity (GR). We apply our general framework to several concrete theories and show that a new theory of spontaneous scalarization with a higher-order scalar kinetic term leaves interesting deviations from GR that can be probed by the observations of gravitational waves emitted from neutron star-black hole binaries. If the scalar mass exceeds the order of typical orbital frequencies ω≃10-13 eV, which is the case for a recently proposed scalarized neutron star with a self-interacting potential, the gravitational waveform practically reduces to that in GR.

AB - In a subclass of Horndeski theories with the speed of gravity equivalent to that of light, we study gravitational radiation emitted during the inspiral phase of compact binary systems. We compute the waveform of scalar perturbations under a post-Newtonian expansion of energy-momentum tensors of pointlike particles that depend on a scalar field. This scalar mode not only gives rise to breathing and longitudinal polarizations of gravitational waves, but it is also responsible for scalar gravitational radiation in addition to energy loss associated with transverse and traceless tensor polarizations. We calculate the Fourier-transformed gravitational waveform of two tensor polarizations under a stationary phase approximation and show that the resulting waveform reduces to the one in a parametrized post-Einsteinian (ppE) formalism. The ppE parameters are directly related to a scalar charge in the Einstein frame, whose existence is crucial to allow the deviation from general relativity (GR). We apply our general framework to several concrete theories and show that a new theory of spontaneous scalarization with a higher-order scalar kinetic term leaves interesting deviations from GR that can be probed by the observations of gravitational waves emitted from neutron star-black hole binaries. If the scalar mass exceeds the order of typical orbital frequencies ω≃10-13 eV, which is the case for a recently proposed scalarized neutron star with a self-interacting potential, the gravitational waveform practically reduces to that in GR.

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U2 - 10.1103/PhysRevD.107.044003

DO - 10.1103/PhysRevD.107.044003

M3 - Article

AN - SCOPUS:85148294078

SN - 2470-0010

VL - 107

JO - Physical Review D

JF - Physical Review D

IS - 4

M1 - 044003

ER -