Chameleon mechanism

Tuesday 28 of October I gave a small!!! talk in physics department,in series of cosmology weekly seminars.

The general title of talk is the Accelerating universe,Theory and phenomenology and the subtitle is Chameleon scalars mechanism and modified gravity.

The general title is the field which I want to be engaged in my Ph.D.thesis.

And what about the chameleon theories?

The accelerating universe open a new paradigm in cosmology.

There are many many models trying to describe this phenomena,but generally we can divided all the models in 2 general subdivisions.

If we accept the context of general relativity, which means that we know gravity well, we will come to the realization that new physical entity needed to describe the accelerating universe,such as cosmological constant or scalar fields generally named quintessence.

The second main models come to existence from the assumption that the general relativity needed to be modified in long ranges and small curvatures.This models named Modified gravity.

But what is chameleon?

The point is that we know that general relativity works well in solar system and local tests of gravity.So if we change the action of Einstein -Hilbert to have new effects in cosmological scales also we will affect the local tests of gravity, so we need a mechanism! in order to conceal this effect in local tests and disappear it and bring it back to existence in cosmological scales. This mechanism is called Chameleon mechanism after the name of lizard!!!like animal which changes its skin color with environment.So the scalar field equivalent to modified gravity /We know about the equivalence of modified gravity with scalar field theories/

changes its behaviour with respect of the density of environment like Chameleons.

BUT

in theoretical point of view this mechanism needs more investigations to be reliable,I will study it more...