Dynamics of scalar perturbations in f(R,T) gravity
  In the context of f(R,T) theories of gravity, we study the evolution of
scalar cosmological perturbations in the metric formalism. According to
restrictions on the background evolution, a specific model within these
theories is assumed in order to guarantee the standard continuity equation.
Using a completely general procedure, we find the complete set of differential
equations for the matter density perturbations. In the case of sub-Hubble
modes, the density contrast evolution reduces to a second-order equation. We
show that for well-motivated f(R,T) Lagrangians the quasistatic approximation
yields to very different results from the ones derived in the frame of the
concordance {\Lambda}CDM model constraining severely the viability of such
theories.
