Tensor perturbations in a general class of Palatini theories
  We study a general class of gravitational theories formulated in the Palatini
approach and derive the equations governing the evolution of tensor
perturbations. In the absence of torsion, the connection can be solved as the
Christoffel symbols of an auxiliary metric which is non-trivially related to
the space-time metric. We then consider background solutions corresponding to a
perfect fluid and show that the tensor perturbations equations (including
anisotropic stresses) for the auxiliary metric around such a background take an
Einstein-like form. This facilitates the study in a homogeneous and isotropic
cosmological scenario where we explicitly establish the relation between the
auxiliary metric and the space-time metric tensor perturbations. As a general
result, we show that both tensor perturbations coincide in the absence of
anisotropic stresses.
