Solar-system tests of the inflation model with a Weyl term

TL;DR

This paper investigates how a Weyl term in modified gravity theories affects solar-system experiments, deriving constraints on the Weyl parameter from light propagation and time delay measurements, notably from the Cassini experiment.

Contribution

It provides the first detailed derivation of light propagation equations in Weyl-modified gravity and constrains the Weyl parameter using solar-system observational data.

Findings

Weyl parameter {b3}_W constrained to less than 0.0015 AU^2 from Cassini data

Relativistic light deflection and Shapiro delay formulas derived for Weyl gravity

Laboratory experiments further limit the Weyl term at small scales

Abstract

Recently, there has been an interest in inflation and modified gravity with a Weyl term added to the general-relativistic action (N. Derulle, M. Sasaki, Y. Sendouda and A. Youssef, JCAP, 3, 040 (2011)). In this paper we study empirical constraint on this modified gravity from solar-system experiments/observations. We first derive linearized equation of motion in the weak field limit and solve it for isolated system in the slow motion limit. We then use it to derive the light propagation equations, and obtain the relativistic Shapiro time delay and the light deflection in one-body central problem. Applying these results to the solar-system measurements, we obtain constraints on the Weyl term parameter {\gamma}_W; the most stringent constraint, which comes from the Cassini relativistic time delay experiment, is for {\gamma}_W to be less than 0.0015 AU^2, or |{\gamma}_W|^(1/2) less than 0.039 AU (19 s). Analysis of precision laboratory gravity experiments put further limit on the Weyl term parameter {\gamma}_W to below the laboratory scale.