323 research outputs found
Conformal anomaly for dilaton coupled electromagnetic field
The derivation of the conformal anomaly for dilaton coupled electromagnetic
field in curved space is presented. The models of this sort naturally appear in
stringy gravity or after spherical reduction of multidimensional
Einstein-Maxwell theory. It is shown that unlike the case of minimal vector in
curved space or dilaton coupled scalar the anomaly induced effective action
cannot be derived. The reason is the same why anomaly induced effective action
cannot be constructed for interacting theories (like QED) in curved space.Comment: Latex file, 10 page
Covariant Generalized Holographic Dark Energy and Accelerating Universe
We proposed the generalized holographic dark energy model where infrared
cutoff is identified with the combination of the FRW universe parameters: the
Hubble rate, particle and future horizons, cosmological constant, the universe
life-time (if finite) and their derivatives. It is demonstrated that with the
corresponding choice of the cutoff one can map such holographic dark energy to
modified gravity or gravity with general fluid. Explicitly, F(R) gravity and
general perfect fluid are worked out in detail and corresponding infrared
cutoff is found. Using this correspondence, we get realistic inflation or
viable dark energy or unified inflationary-dark energy universe in terms of
covariant holographic dark energy.Comment: LaTeX 9 pages, version to appear in EPJ
Dark Energy: the equation of state description versus scalar-tensor or modified gravity
Dark energy dynamics of the universe can be achieved by equivalent
mathematical descriptions taking into account generalized fluid equations of
state in General Relativity, scalar-tensor theories or modified F(R) gravity in
Einstein or Jordan frames. The corresponding technique transforming equation of
state description to scalar-tensor or modified gravity is explicitly presented.
We show that such equivalent pictures can be discriminated by matching
solutions with data capable of selecting the true physical frame.Comment: LaTeX file, 10 pages, 3 figures, the fit of two equivalent models
with observational data is added, new reference
Newton potential in deSitter braneworld
Using graviton correlator on deSitter (dS) brane in 5d AdS or dS bulk we calculate the four-dimensional Newton potential. For flat brane in AdS bulk the Randall-Sundrum result is recovered. For flat brane in dS bulk the sign of subleading () term in Newton potential is negative if compare with AdS bulk. In accordance with dS/CFT correspondence this indicates that dual CFT should be non-unitary (for example, higher derivative conformal theory)
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