Strong Lensing, Compact Objects and Dark Energy

Any Dark Energy model other than the Cosmological Constant has to show clustering at some scales and even some unified dark matter models in the clustering regime behave effectively as negative pressure perfect fluids .With this fact in mind, as a first step we will discuss various properties of static configurations of negative pressure perfect fluids with linear equation of state in General Relativistic context and also discuss behavior of photons in such a geometry. We will also discuss a scheme proposed by Bozza for calculating  various lensing observables in the strong deflection limit and apply it to some metrics of our interest including some static spherically symmetric solutions in 'geometric Dark Energy' models.