Cosmological inviability of f (R, T) gravity

Among many alternative gravitational theories to General Relativity (GR), f(R, T) gravity (where R is the Ricci scalar and T the trace of the energy-momentum tensor) has been widely studied recently. By adding a matter contribution to the gravitational Lagrangian, f(R, T) theories have become an interesting extension to GR displaying a broad phenomenology in astrophysics and cosmology. In this paper, we discuss, however, the difficulties appearing in explaining a viable and realistic cosmology within the f(R, T) class of theories. Our results challenge the viability of f(R, T); as an alternative modification of gravity.