Cosmological constraints on post-Newtonian parameters in effectively massless scalar-tensor theories of gravity
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Date
2019
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Abstract
We study the cosmological constraints on the variation of Newton’s constant and on post-Newtonian
parameters for simple models of the scalar-tensor theory of gravity beyond the extended Jordan-BransDicke theory. We restrict ourselves to an effectively massless scalar field with a potential V ∝ F2, where
FðσÞ ¼ N2
pl þ ξσ2 is the coupling to the Ricci scalar considered. We derive the theoretical predictions for
cosmic microwave background anisotropies and matter power spectra by requiring that the effective
gravitational strength at present is compatible with the one measured in a Cavendish-like experiment and by
assuming an adiabatic initial condition for scalar fluctuations. When comparing these models with Planck
2015 and a compilation of baryonic acoustic oscillations data, all these models accommodate a
marginalized value for H0 higher than in ΛCDM. We find no evidence for a statistically significant
deviation from Einstein’s general relativity. We find ξ < 0.064 (jξj < 0.011) at 95% CL for ξ > 0 (for
ξ < 0, ξ ≠ −1=6). In terms of post-Newtonian parameters, we find 0.995 < γPN < 1 and 0.99987 <
βPN < 1 (0.997 < γPN < 1 and 1 < βPN < 1.000011) for ξ > 0 (for ξ < 0). For the particular case of the
conformal coupling, i.e., ξ ¼ −1=6, we find constraints on the post-Newtonian parameters of similar
precision to those within the Solar System.
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Keywords
Newton’s constant, Cosmic microwave, Cavendish experiment, Jordan-BransDicke theory
Citation
Rossi, M. et al. (2019) Cosmological constraints on post-Newtonian parameters in effectively massless scalar-tensor theories of gravity. Physical review. D. [Online] 100 (10), 1–.https://doi.org/10.1103/PhysRevD.100.103524