Solar system constraints on alternative gravity theories

TL;DR

This paper investigates how alternative gravity theories, inspired by string theory, can be constrained by solar system observations such as perihelion precession and light bending, highlighting the influence of stringy effects.

Contribution

It provides a detailed analysis of solar system constraints on various string-inspired and quadratic gravity models, including bounds on their coupling parameters.

Findings

Dilaton field effects dominate light bending in string-inspired models.

Similar results are found in quadratic gravity solutions.

Numerical bounds on coupling parameters are estimated from observational data.

Abstract

The perihelion precession of planetary orbits and the bending angle of null geodesics are estimated for different gravity theories in string-inspired models. It is shown that, for dilaton coupled gravity, the leading order measure in the angle of bending of light comes purely from vacuum expectation value of the dilaton field which may be interpreted as an indicator of a dominant stringy effect over the curvature effect. We arrive at similar results for spherically symmetric solution in quadratic gravity. We also present the perihelion shift and bending of light in the Einstein-Maxwell-Gauss-Bonnet theory with special reference to the Casimir effect and Damour-Polyakov mechanism. Numerical bounds to different coupling parameters in these models are estimated.