Matter may matter

@article{Haghani2014MatterMM,
  title={Matter may matter},
  author={Zahra Haghani and Tiberiu Harko and Hamid Reza Sepangi and Shahab Shahidi},
  journal={International Journal of Modern Physics D},
  year={2014},
  volume={23},
  pages={1442016}
}
We propose a gravitational theory in which the effective Lagrangian of the gravitational field is given by an arbitrary function of the Ricci scalar, the trace of the matter energy–momentum tensor, and the contraction of the Ricci tensor with the matter energy–momentum tensor. The matter energy–momentum tensor is generally not conserved, thus leading to the appearance of an extra-force, acting on massive particles in a gravitational field. The stability conditions of the theory with respect to… Expand
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