期刊
PHYSICAL REVIEW D
卷 91, 期 10, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevD.91.104003
关键词
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资金
- Consolider-Ingenio MULTIDARK [CSD2009-00064]
- Wallonia-Brussels Federation Grant ARC [11/15-040]
- A*MIDEX Project - Investissements d'Avenir French Government program [ANR-11-IDEX-0001-02]
- MINECO (Spain) [FPA2011-27853-C02-01, FPA2014-53375-C2-1-P, FIS2011-23000]
We discuss the consistency of a recently proposed class of theories described by an arbitrary function of the Ricci scalar, the trace of the energy-momentum tensor, and the contraction of the Ricci tensor with the energy-momentum tensor. We briefly discuss the limitations of including the energy-momentum tensor in the action, as it is a nonfundamental quantity but a quantity that should be derived from the action. The fact that theories containing nonlinear contractions of the Ricci tensor usually lead to the presence of pathologies associated with higher-order equations of motion will be shown to constrain the stability of this class of theories. We provide a general framework and show that the conformal and nonminimal couplings to the matter fields usually lead to higher-order equations of motion. To illustrate such limitations, we explicitly study the cases of a canonical scalar field, a K-essence field, and a massive vector field, whereas for the scalar field cases, it is possible to find healthy theories, and for the vector field case, the presence of instabilities is unavoidable.
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