Abstract
In Yang-Mills gravity based on flat space-time, the eikonal equation for a light ray is derived from the modified Maxwell’s wave equations in the geometric-optics limit. One obtains a Hamilton-Jacobi type equation, G L µv ∂ µ Ψ ∂ v Ψ = 0 with an effective Riemannian metric tensor G L µv . According to Yang-Mills gravity, light rays (and macroscopic objects) move as if they were in an effective curved space-time with a metric tensor. The deflection angle of a light ray by the sun is about 1.53″ for experiments with optical frequencies ≈ 10 14 Hz. It is roughly 12% smaller than the usual value 1.75″. However, the experimental data in the past 100 years for the deflection of light by the sun in optical frequencies have uncertainties of (10-20)% due to large systematic errors. If one does not take the geometric-optics limit, one has the equation, G L µv [ ∂ µ Ψ ∂ v Ψ cos Ψ+ ( ∂ µ ∂ v Ψ) sin Ψ] = 0, which suggests that the deflection angle could be frequency-dependent, according to Yang-Mills gravity. Nowadays, one has very accurate data in the radio frequencies ≈ 10 9 Hz with uncertainties less than 0.1%. Thus, one can test this suggestion by using frequencies ≈ 10 12 Hz, which could have a small uncertainty 0.1% due to the absence of systematic errors in the very long baseline interferometry.