Comment on “<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>f</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mi>R</mml:mi><mml:mo>,</mml:mo><mml:mi>T</mml:mi><mml:mo stretchy="false">)</mml:mo></mml:math>gravity”

In Phys. Rev. D 84, 024020 (2011) Harko, Lobo, Nojiri and Odintsov presented a modified theory of gravitation, $f(R,T)$ gravity, where the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and of the trace of the stress-energy tensor. In this Comment we correct the conservation equation of the stress-energy tensor, since we noticed that the authors missed an essential term which has consequences in the equation of motion of test particles. We thus correct the derivation of this equation of motion and comment on some of its consequences.

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