Classification of Gravitational Theories

[sadegh4137]

hi

there are many gravitational theories such as
1- modified gravity { massive gravity, dilaton gravity, ... }
2-conformal gravity
3-emergent gravity
4-lower and highest dimensional gravity
5-...

is anybody know about this gravitational theories?
is there a general classification of these theories that tell us all of these theories and state the features and properties of these?
are these related to petrov classification that states http://en.wikipedia.org/wiki/Petrov_classification

Thanks

 

[Mentz114]

The theories you list are different from GR, and the Petrov classification is for vacuum solutions in GR.

So, no the Petrov classification is not about these different theories.

You might like to start here

http://en.wikipedia.org/wiki/Alternatives_to_general_relativity

 

[Bill_K]

the Petrov classification is for vacuum solutions in GR.

Non-vacuum as well. In either case it pertains to the eigenvectors of the Weyl tensor. The Reissner-Nordstrom solution, for example, is Type D.