Solar system constraints on alternative gravity theories

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 a 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.

Figure 1

The figure shows the variation of the perihelion shift with charge.

Figure 2

The figure shows the variation of perihelion shift with a dilaton field for different choices of $Q$ and $M$.

Figure 3

The figure shows the variation of bending of light with a dilaton strength for different choices of mass and charge.