Scattering of Photons by an External Gravitational Field in the Framework of Higher-Derivative Gravity

The scattering of photons by a static gravitational field, treated as an external field, is discussed in the context of gravity with higher derivatives. It is shown that the R2 sector of the theory does not contribute to the photon scattering, whereas the R2µν sector produces dispersive (energy-dependent) photon propagation. The deflection of light by a gravitational field was one of the most striking predictions of general relativity. The observation of this effect was also one of the earliest experimental verifications of Einstein’s theory. According to the equivalence principle, photons fall freely along light-like geodesics in curved spacetime, and al