A bimetric theory of gravity

I will motivate and describe a theory of gravity in the presence of a second spin 2 field which does not suffer from the usual ghost instabilities prevalent in such theories. I will outline the Hamiltonian analysis that shows the absence of the ghost mode in this theory. Then I will focus on some potential problems besides the ghost problem and explain the nontrivial role that general covariance plays in avoiding the problems and ensuring that the theory is well defined. I will end with some comments on causality and spacetime in such theories.