Equivalence Principle (EP) and Solar System Constraints on $R(1\pm \epsilon \ln({R \over R_c}))$ model of Gravity

TL;DR

This paper investigates a modified gravity model with a logarithmic correction, demonstrating it can satisfy solar system constraints, equivalence principle tests, and chameleon screening mechanisms for very small epsilon values.

Contribution

It analyzes a specific $f(R)$ gravity model with a logarithmic term, showing it meets experimental constraints and the chameleon mechanism's conditions.

Findings

Model's $eta$ parameter is suppressed by the chameleon mechanism.

The PPN parameter $\gamma_{PPN}$ is consistent with experiments.

The model is viable for $\epsilon acksimeq 10^{-14}$.

Abstract

Experiments on the violation of equivalence principle (EP) and solar system give a number of constraints in which any modified gravity model must satisfy them. We study these constraints on a kind of $f(R)$ gravity as $f(R) = R(1\pm \epsilon \ln({R \over R_c}))$. For this investigation we use of chameleon mechanism and show that a spherically body has thin-shell in this model. So that we obtain an effective coupling of the fifth force which is suppressed through a chameleon mechanism. Also, we obtain $\gamma_{PPN} = 1 \pm 1.13 \times10^{-5}$ which is agreement with experiment results. At last, we show that for $R_c \thickapprox \rho_c$ this model is consistent with EP, thin shell condition and fifth force of chameleon mechanism for $\epsilon \backsimeq 10^{-14}$.