2,501 research outputs found
Quantum generation of Schwarzschild-de Sitter (Nariai) black holes in effective dilaton-Maxwell gravity
Dilaton coupled electromagnetic field is essential element of low-energy
string effective action or it may be considered as result of spherical
compactification of Maxwell theory in higher dimensions. The large and
large curvature effective action for dilaton coupled vectors is calculated.
Adding such quantum correction to classical dilaton gravity action we show that
effective dilaton-Maxwell gravity under consideration may generate
Schwarzschild-de Sitter black holes (SdS BHs) with constant dilaton as
solutions of the theory. That suggests a mechanism (alternative to BHs
production) for quantum generation of SdS BHs in early universe (actually, for
quantum creation of inflationary Universe) due to back-reaction of dilaton
coupled matter. The possibility of proliferation of anti-de Sitter space is
briefly discussed.Comment: LaTeX file, 11 page
Thermodynamics of Schwarzschild-(Anti-)de Sitter Black Holes with account of quantum corrections
We discuss the quantum corrections to thermodynamics (and geometry) of S(A)dS
BHs using large one-loop anomaly induced effective action for dilaton
coupled matter (scalars and spinors). It is found the temperature, mass and
entropy with account of quantum effects for multiply horizon SdS BH and SAdS BH
what also gives the corresponding expressions for their limits: Schwarzschild
and de Sitter spaces. In the last case one can talk about quantum correction to
entropy of expanding Universe.
The anomaly induced action under discussion corresponds to 4d formulation
(s-wave approximation, 4d quantum matter is minimal one) as well as 2d
formulation (complete effective action, 2d quantum matter is dilaton coupled
one). Hence, most of results are given for the same gravitational background
with interpretation as 4d quantum corrected BH or 2d quantum corrected
dilatonic BH. Quantum aspects of thermodynamics of 4d 't Hooft BH model are
also considered.Comment: LaTeX file, 28 pages, some misprints are correcte
Modified f(R) gravity from scalar-tensor theory and inhomogeneous EoS dark energy
The reconstruction of f(R)-gravity is showed by using an auxiliary scalar
field in the context of cosmological evolution, this development provide a way
of reconstruct the form of the function f (R) for a given evolution of the
Hubble parameter. In analogy, f(R)-gravity may be expressed by a perfect fluid
with an inhomogeneous equation of state that depends on the Hubble parameter
and its derivatives. This mathematical equivalence that may confuse about the
origin of the mechanism that produces the current acceleration, and possibly
the whole evolution of the Hubble parameter, is shown here.Comment: 8 page
Tachyon fields with effects of quantum matter in an Anti-de Sitter Universe
We consider an Anti-de Sitter universe filled by quantum conformal matter
with the contribution from the usual tachyon and a perfect fluid. The model
represents the combination of a trace-anomaly annihilated and a tachyon driven
Anti-de Sitter universe. The influence exerted by the quantum effects and by
the tachyon on the AdS space is studied. The radius corresponding to this
universe is calculated and the effect of the tachyon potential is discussed, in
particular, concerning to the possibility to get an accelerated scale factor
for the proposed model (implying an accelerated expansion of the AdS type of
universe). Fulfillment of the cosmological energy conditions in the model is
also investigatedComment: 14 Latex pages, no figure
Trace anomaly induced effective action and 2d black holes for dilaton coupled supersymmetric theories
The action for 2d dilatonic supergravity with dilaton coupled matter and
dilaton multiplets is constructed. Trace anomaly and anomaly induced effective
action (in components as well as in supersymmetric form) for matter
supermultiplet on bosonic background are found. The one-loop effective action
and large- effective action for quantum dilatonic supergravity are also
calculated. Using induced effective action one can estimate the back-reaction
of dilaton coupled matter to the classical black hole solutions of dilatonic
supergravity. That is done on the example of supersymmetric CGHS model with
dilaton coupled quantum matter where Hawking radiation which turns out to be
zero is calculated. Similar 2d analysis maybe used to study spherically
symmetric collapse for other models of 4d supergravity.Comment: 21 pages, LaTeX, NDA-FP-3
String versus Einstein frame in an AdS/CFT induced quantum dilatonic brane-world universe
AdS/CFT induced quantum dilatonic brane-world where 4d boundary is flat or de
Sitter (inflationary) or Anti-de Sitter brane is considered. The classical
brane tension is fixed but boundary QFT produces the effective brane tension
via the account of corresponding conformal anomaly induced effective action.
This results in inducing of brane-worlds in accordance with AdS/CFT set-up as
warped compactification. The explicit, independent construction of quantum
induced dilatonic brane-worlds in two frames: string and Einstein one is done.
It is demonstrated their complete equivalency for all quantum cosmological
brane-worlds under discussion, including several examples of classical
brane-world black holes. This is different from quantum corrected 4d dilatonic
gravity where de Sitter solution exists in Einstein but not in Jordan (string)
frame. The role of quantum corrections on massive graviton perturbations around
Anti-de Sitter brane is briefly discussed.Comment: LaTeX file, 24 pages, minor changes to match with published versio
Viscous Fluids and Gauss-Bonnet Modified Gravity
We study effects of cosmic fluids on finite-time future singularities in
modified -gravity, where and are the Ricci scalar and the
Gauss-Bonnet invariant, respectively. We consider the fluid equation of state
in the general form, , and we suppose the existence of a
bulk viscosity. We investigate quintessence region () and phantom
region () and the possibility to change or avoid the singularities
in -gravity. Finally, we study the inclusion of quantum effects in
large curvatures regime.Comment: 14 page
Magnetic characterization of the frustrated three-leg ladder compound [(CuCl2tachH)3Cl]Cl2
We report the magnetic features of a new one-dimensional stack of
antiferromagnetically coupled equilateral copper(II) triangles. High-field
magnetization measurements show that the interaction between the copper
triangles is of the same order of magnitude as the intra-triangle exchange
although only coupled via hydrogen bonds. The infinite chain turns out to be an
interesting example of a frustrated cylindrical three-leg ladder with competing
intra- and inter-triangle interactions. We demonstrate that the ground state is
a spin singlet which is gaped from the triplet excitation.Comment: 6 pages, 9 figures, revised version submitted to Phys. Rev. B. More
information at http://obelix.physik.uni-osnabrueck.de/~schnack
Supersymmetric new brane-world
The quantum-induced dilatonic brane world (New Brane World) is created by
brane CFT quantum effects (giving effective brane tension) in accordance with
AdS/CFT set-up which also defines surface term. Considering the bosonic sector
of 5d gauged supergravity with single scalar and taking the boundary action as
predicted by supersymmetry, the possibility to supersymmetrize dilatonic New
Brane World is discussed. It is demonstrated that for a number of
superpotentials the flat SUSY dilatonic brane-world (with dynamically induced
brane dilaton) or quantum-induced de Sitter dilatonic brane-world (not Anti-de
Sitter one) where SUSY is broken by the quantum effects occurs. The analysis of
graviton perturbations indicates that gravity is localized on such branes.Comment: LaTeX 16 pages, misprints are correcte
Accelerating universe from F(T) gravity
It is shown that the acceleration of the universe can be understood by
considering a F(T) gravity models. For these F(T) gravity models, a variant of
the accelerating cosmology reconstruction program is developed. Some explicit
examples of F(T) are reconstructed from the background FRW expansion history.Comment: 13 pages, references adde
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