Binary systems in Palatini-f(R) gravity

TL;DR

This paper investigates binary systems within Palatini-f(R) gravity, calculating post-Newtonian parameters and demonstrating that black hole binaries behave identically to those in general relativity due to redefined masses.

Contribution

It provides a detailed method to incorporate Palatini-f(R) modifications into the DIRE formalism and confirms black hole binaries are observationally indistinguishable from GR.

Findings

Black hole binaries can be described by redefined masses, making them identical to GR systems.

The formalism correctly accounts for Palatini modifications within the post-Newtonian framework.

Observational differences from GR are negligible for black hole binaries.

Abstract

We consider compact binary systems in f(R) gravity theories in the Palatini approach and calculate the post-Newtonian parameters to the 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 Einsteins gravity with 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.