Extreme- and intermediate-mass ratio inspirals in dynamical Chern-Simons modified gravity

Carlos F. Sopuerta and Nicolás Yunes
Phys. Rev. D 80, 064006 – Published 2 September 2009

Abstract

Chern-Simons modified gravity is a four-dimensional, effective theory that descends both from string theory and loop quantum gravity, and that corrects the Einstein-Hilbert action by adding the product of a scalar field and the parity-violating, Pontryagin density. The Chern-Simons modification deforms the gravitational field of spinning black holes, which is now described by a modified Kerr geometry whose multipole moments deviate from the Kerr ones only at the fourth multipole =4. This paper investigates possible signatures of this theory in the gravitational-wave emission produced in the inspiral of stellar compact objects into massive black holes, both for intermediate- and extreme-mass ratios. We use the semirelativistic approximation, where the trajectory of the small compact object is modeled via geodesics of the massive black hole geometry, while the gravitational waveforms are obtained from a multipolar decomposition of the radiative field. The main Chern-Simons corrections to the waveforms arise from modifications to the geodesic trajectories, which in turn are due to changes to the massive black hole geometry, and manifest themselves as an accumulating dephasing relative to the general relativistic case. We also explore the propagation and the stress-energy tensor of gravitational waves in this theory, using the short-wavelength approximation. We find that, although this tensor has the same form as in general relativity, the energy and angular momentum balance laws are indeed modified through the stress-energy tensor of the Chern-Simons scalar field. These balance laws could be used to describe the inspiral through adiabatic changes in the orbital parameters, which in turn would enhance the dephasing effect. Gravitational-wave observations of intermediate- or extreme-mass-ratio inspirals with advanced ground detectors or with the Laser Interferometer Space Antenna could use such dephasing to test the dynamical theory to unprecedented levels, thus beginning the era of gravitational-wave tests of effective quantum gravity theories.

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  • Received 28 April 2009

DOI:https://doi.org/10.1103/PhysRevD.80.064006

©2009 American Physical Society

Authors & Affiliations

Carlos F. Sopuerta1 and Nicolás Yunes2

  • 1Institut de Ciències de l’Espai (CSIC-IEEC), Facultat de Ciències, Campus UAB, Torre C5 parells, Bellaterra, 08193 Barcelona, Spain
  • 2Physics Department, Princeton University, Princeton, New Jersey 08544, USA

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Vol. 80, Iss. 6 — 15 September 2009

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