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.