2 research outputs found
Modified F(R) Horava-Lifshitz gravity: a way to accelerating FRW cosmology
We propose a general approach for the construction of modified gravity which
is invariant under foliation-preserving diffeomorphisms. Special attention is
paid to the formulation of modified Ho\v{r}ava-Lifshitz gravity (FRHL),
whose Hamiltonian structure is studied. It is demonstrated that the
spatially-flat FRW equations of FRHL are consistent with the constraint
equations. The analysis of de Sitter solutions for several versions of FRHL
indicates that the unification of the early-time inflation with the late-time
acceleration is possible. It is shown that a special choice of parameters for
FRHL leads to the same spatially-flat FRW equations as in the case of
traditional -gravity. Finally, an essentially most general modified
Ho\v{r}ava-Lifshitz gravity is proposed, motivated by its fully
diffeomorphism-invariant counterpart, with the restriction that the action does
not contain derivatives higher than the second order with respect to the time
coordinate.Comment: LaTeX 11 pages. v4: Some errors have been correcte
Thin accretion disk signatures of slowly rotating black holes in Ho\v{r}ava gravity
In the present work, we consider the possibility of observationally testing
Ho\v{r}ava gravity by using the accretion disk properties around slowly
rotating black holes of the Kehagias-Sfetsos solution in asymptotically flat
spacetimes. The energy flux, temperature distribution, the emission spectrum as
well as the energy conversion efficiency are obtained, and compared to the
standard slowly rotating general relativistic Kerr solution. Comparing the mass
accretion in a slowly rotating Kehagias-Sfetsos geometry in Ho\v{r}ava gravity
with the one of a slowly rotating Kerr black hole, we verify that the intensity
of the flux emerging from the disk surface is greater for the slowly rotating
Kehagias-Sfetsos solution than for rotating black holes with the same
geometrical mass and accretion rate. We also present the conversion efficiency
of the accreting mass into radiation, and show that the rotating
Kehagias-Sfetsos solution provides a much more efficient engine for the
transformation of the accreting mass into radiation than the Kerr black holes.
Thus, distinct signatures appear in the electromagnetic spectrum, leading to
the possibility of directly testing Ho\v{r}ava gravity models by using
astrophysical observations of the emission spectra from accretion disks.Comment: 12 pages, 15 figures. V2: 13 pages, clarifications and discussion
added; version accepted for publication in Classical and Quantum Gravit