Binary systems in Palatini $f(R)$ gravity

Binary systems in Palatini $f (R)$ gravity

Kari Enqvist, Hannu J. Nyrhinen, and Tomi Koivisto

Phys. Rev. D 88, 104008 – Published 12 November 2013

Abstract

We consider compact binary systems in $f (R)$ gravity theories in the Palatini approach and calculate the post-Newtonian parameters to 1.5PN order using the method of direct integration of the relaxed Einstein equations (DIRE). The Palatini-type modifications of gravity can be formulated as Einstein’s gravity with a modified response to matter sources, and it is shown in detail how to treat these correctly within the DIRE formalism. Our results explicitly confirm the expectation that for binary black holes the new effects can be absorbed into redefinitions of the binary masses, rendering such systems observationally identical to general relativity.

Received 27 August 2013

DOI:https://doi.org/10.1103/PhysRevD.88.104008

Authors & Affiliations

Kari Enqvist^* and Hannu J. Nyrhinen^†

Department of Physics, University of Helsinki and Helsinki Institute of Physics, P.O. Box 64, FI-00014 Helsinki, Finland

Tomi Koivisto^‡

Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, N-0315 Oslo, Norway

^*kari.enqvist@helsinki.fi
^†hannu.nyrhinen@helsinki.fi
^‡tomik@astro.uio.no

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Vol. 88, Iss. 10 — 15 November 2013

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