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Linearized f(R) Gravity: Gravitational Radiation & Solar System Tests | | Christopher P. L. Berry
; Jonathan R. Gair
; | | Date: |
5 Apr 2011 | | Abstract: | We investigate the linearized form of metric f(R)-gravity, assuming that f(R)
is analytic about R = 0 so it may be expanded as f(R) = R + a_2 R^2/2 + ...
Gravitational radiation is modified, admitting an extra mode of oscillation,
that of the Ricci scalar. We derive an effective energy-momentum tensor for the
radiation. We also present weak-field metrics for simple sources. These
demonstrate that Kerr (or Schwarzschild) black holes do not exist in
f(R)-gravity. We apply the metrics to tests that could constrain f(R). We show
that light deflection experiments cannot distinguish f(R)-gravity from general
relativity as both have an effective post-Newtonian parameter gamma = 1. We
find that planetary precession rates are enhanced relative to general
relativity; from the orbit of Mercury we derive the bound |a_2| < 1.2 imes
10^{18} m^2. Gravitational wave astronomy may be more useful: considering the
phase of a gravitational waveform we estimate deviations from general
relativity could be measurable for an extreme-mass-ratio inspiral about a 10^6
M_sol black hole if |a_2| > 10^{17} m^2. However Eot-Wash experiments provide
the strictest bound |a_2| < 2 imes 10^{-9} m^2. Although the astronomical
bounds are weaker, they are still of interest in the case that the effective
form of f(R) is modified in different regions, perhaps through the chameleon
mechanism. Assuming the laboratory bound is universal, we conclude that the
propagating Ricci scalar mode cannot be excited by astrophysical sources. | | Source: | arXiv, 1104.0819 | | Services: | Forum | Review | PDF | Favorites | |
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