Strong lensing as a test for alternative theories of gravity

Abstract

Gravitational Lensing was predicted by Albert Einstein from his General Theory of Relativity. The phenomenon describes the bending of light at the vicinity of an intermediate mass between the source and an observer. Gravitational Lensing was confirmed to occur when observations showed that light from a distant star was deflected by the Sun, and thus Einstein's General Theory of Relativity became widely accepted. However when the deflection of light is caused by larger masses such as a cluster of galaxies, the predictions from General Theory of Relativity deviate from observations. The discrepancies are accounted for by including dark matter mass in the equations so as to match observations. Nonetheless other theories of gravity have been and are still being proposed as an alternative to Einstein's General Theory of Relativity. The theories considered in this project were Conformal Weyl Gravity and TeVeS which were tested using Strong Gravitational Lensing to understand whether their numerical predictions can match observations without invoking dark matter. Their respective constants were constrained and then compared to the outcome from another test which the two theories were subjected to. In fact Conformal Weyl Gravity's constant (y) obtained from this study did not match with that obtained from the study of the relation between the rotational velocities of galaxies and the distance from the galaxy center. Thus Conformal Weyl Gravity cannot explain two different phenomena without dark matter using the same value for y. On the other hand TeVeS Milgrom's constant (a0) did not vary by much and the factor by which it varied was predicted by other studies. Therefore comparing the two theories of gravity, the principles behind TeVeS are more adapt than those in Conformal Weyl Gravity.