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# Modified F(R) Hořava–Lifshitz gravity: a way to accelerating FRW cosmology

Classical and Quantum Gravity (Impact Factor: 3.56). 08/2010; 27(18):185021. DOI: 10.1088/0264-9381/27/18/185021

Source: arXiv

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**ABSTRACT:**In order to explore some general features of modified theories of gravity which involve higher derivatives and spontaneous Lorentz and/or diffeomorphism symmetry breaking, we study the recently proposed new version of covariant renormalizable gravity (CRG). CRG attains power-counting renormalizability via higher derivatives and introduction of a constrained scalar field and spontaneous symmetry breaking. We obtain an Arnowitt-Deser-Misner representation of the CRG action in four-dimensional spacetime with respect to a foliation of spacetime adapted to the constrained scalar field. The resulting action is analyzed by using Hamiltonian formalism. We discover that CRG contains two extra degrees of freedom. One of them carries negative energy (a ghost) and it will destabilize the theory due to its interactions. This result is in contrast with the original paper [Phys. Lett. B 701, 117 (2011), arXiv:1104.4286 [hep-th]], where it was concluded that the theory is free of ghosts and renormalizable when we analyze fluctuations on the flat background.Physical review D: Particles and fields 08/2012; 87(6). -
##### Article: Fermion analysis of IR modified Hořava–Lifshitz gravity: tunneling and perturbation perspectives

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**ABSTRACT:**In this paper, we investigate the fermion Hawking radiation and quasinormal (QN) modes in infrared (IR) modified Hořava–Lifshitz (HL) gravity under tunneling and perturbation perspectives. Firstly, through the fermion tunneling in IR modified HL gravity, we obtain the Hawking radiation emission rate, tunneling temperature and entropy for the Kehagias–Sfetsos black hole. It is found that the results of fermion tunneling are consistent with the thermodynamics results obtained by calculating surface gravity. Secondly, we numerically calculate the low-lying QN mode frequencies of fermion perturbations by using WKB formulas including the third-order and sixth-order approximations simultaneously. It turns out that the actual frequency of fermion perturbation is larger than that in the Schwarzschild case, and the damping rate is smaller than that for the pure Schwarzschild. The results of fermion perturbation suggest the QN modes could live longer in HL gravity.Classical and Quantum Gravity 05/2011; 28(12):125024. · 3.56 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**In this paper we study the relation between F(R) and scalar-tensor Hořava-Lifshitz gravity. We find that due to the broken diffeomorphism invariance which is a characteristic property of Hořava-Lifshitz gravities corresponding scalar-tensor theory that is related to F(R) Hořava-Lifshitz gravity by specific Weyl transformation has a more complicated form than in the case of the full diffeomorphism invariant F(R) theory of gravity and its scalar-tensor formulation. We also show that in the low energy limit this theory reduces to the relativistic scalar-tensor theory of gravity.Physical review D: Particles and fields 11/2011; 84(10).

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