Viability of vector-tensor theories of gravity

Understand

We present a detailed study of the viability of general vector-tensor theories of gravity in the presence of an arbitrary temporal background vector field.

• We find that there are six different classes of theories which are indistinguishable from General Relativity by means of local gravity experiments.
• We study the propagation speeds of scalar, vector and tensor perturbations and obtain the conditions for classical stability of those models.
• We compute the energy density of the different modes and find the conditions for the absence of ghosts in the quantum theory.