Post-Newtonian parameters and cosmological constant of screened modified gravity

TL;DR

This paper derives key gravitational and cosmological parameters for screened modified gravity theories, analyzing their dependence on model specifics and applying results to constrain models using solar system and cosmological data.

Contribution

It provides a general framework to calculate PPN parameters and the cosmological constant for SMG models with various potentials and couplings, including specific theories like chameleon, symmetron, and dilaton.

Findings

Derived formulas for PPN parameters and effective cosmological constant in SMG.

Constrained model parameters using combined solar system and cosmological observations.

Analyzed dependence of parameters on model specifics and source properties.

Abstract

Screened modified gravity (SMG) is a kind of scalar-tensor theories with screening mechanisms, which can generate screening effect to suppress the fifth force in high density environments and pass the solar system tests. Meanwhile, the potential of scalar field in the theories can drive the acceleration of the late universe. In this paper, we calculate the parameterized post-Newtonian (PPN) parameters $\gamma$ and $\beta$, the effective gravitational constant $G_{\rm eff}$ and the effective cosmological constant $\Lambda$ for SMG with a general potential $V$ and coupling function $A$. The dependence of these parameters on the model parameters of SMG and/or the physical properties of the source object are clearly presented. As an application of these results, we focus on three specific theories of SMG (chameleon, symmetron and dilaton models). Using the formulae to calculate their PPN parameters and cosmological constant, we derive the constraints on the model parameters by combining the observations on solar system and cosmological scales.