https://dspace.library.uu.nl/bitstream/handle/1874/4816/13838.pdf?sequence=2

Massive and mass-less Yang-Mills and gravitational fields

On ghost-free tensor lagrangians and linearized gravitation

For ultra compact objects, light rings and fundamental photon orbits (FPOs) play a pivotal role in the theoretical analysis of strong gravitational lensing effects, and of BH shadows in particular. In this short review, specific models are considered to illustrate how FPOs can be useful in order to understand some non-trivial gravitational lensing effects. This paper aims at briefly overviewing the theoretical foundations of these effects, touching also some of the related phenomenology, both in general relativity and alternative theories of gravity, hopefully providing some intuition and new insights for the underlying physics, which might be critical when testing the Kerr black hole hypothesis.

Shadows and strong gravitational lensing: a brief review

Classical general relativity derived from quantum gravity

Inconsistency of finite range gravitation

We have used radio interferometry to measure the deflection of a radio source as it passed the sun. This deflection is a separable combination of refraction in the coronal electron plasma and the general relativistic effect. The observed deflection was ${1.04}_{\ensuremath{-}0.10}^{+0.15}$ times that predicted by Einstein's theory of general relativity. The observation also yielded a reasonable value for the coronal electron density.

Radio Interferometric Test of the General Relativistic Light Bending Near the Sun

: Radio interferometry was used to measure the deflection of a radio source as it passed the Sun. This deflection is a separable combination of refraction in the coronal electron plasma and the General Relativistic effect. The observed inverse distance component was 1.04(+0.15/-0.10) of that predicted by Einstein's theory of General Relativity. The observation also yielded a reasonable value for the coronal electron density. (Author)

R. D. Ekers

Papers

Radio Interferometric Test of the General Relativistic Light Bending Near the Sun

A radio interferometric test of the general relativistic light bending near the sun