1,609 research outputs found
Plane symmetric solutions in Horava-Lifshitz theory
The purpose of this paper is to find and analyze plane symmetric, static(non
static) solutions in Ho\v{r}ava- Lifshitz gravity. We discussed two versions of
Horava gravity. First we showed that if the detailed balance principle have
considered, there are both static and non-static solutions. We show that in
static case there are two family of solvable models which either of them has a
well defined EOS, in analogous to the perfect fluid solutions in GR. In
non-static case we find a family of solutions. Some physical properties of
these solutions was discussed. Secondly we investigated the plane symmetric
solutions for a new modified version of Ho\v{r}avaa gravity \cite{bla}, which
has the new terms inserted action in it.Comment: 16 pages, no figure, references added, re-organized and re-writtend,
typos corrected, main results unchange
Atomic quadrature squeezing and quantum state transfer in a hybrid atom-optomechanical cavity with two Duffing mechanical oscillators
In this paper, we investigate theoretically the quantum state transfer in a
laser driven hybrid optomechanical cavity with two Duffing-like anharmonic
movable end mirrors containing an ensemble of identical two-level trapped
atoms. The quantum state transfer from the Bogoliubov modes of the two
anharmonic oscillators to the atomic mode results in the atomic quadrature
squeezing beyond the standard quantum limit of 3 dB which can be controlled by
both the optomechanical and atom-field coupling strengths. Interestingly, the
generated atomic squeezing can be made robust against the noise sources by
means of the Duffing anharmonicity. Moreover, the results reveal that the
presence of the Duffing anharmonicity provides the possibility of transferring
strongly squeezed states between the two mechanical oscillators in a short
operating time and with a high fidelity
Steady-state mechanical squeezing and ground-state cooling of a Duffing anharmonic oscillator in an optomechanical cavity assisted by a nonlinear medium
In this paper, we study theoretically a hybrid optomechanical system
consisting of a degenerate optical parametric amplifier inside a driven optical
cavity with a moving end mirror which is modeled as a stiffening Duffing-like
anharmonic quantum mechanical oscillator. By providing analytical expressions
for the critical values of the system parameters corresponding to the emergence
of the multistability behavior in the steady-state response of the system, we
show that the stiffening mechanical Duffing anharmonicity reduces the width of
the multistability region while the optical parametric nonlinearity can be
exploited to drive the system toward the multistability region. We also show
that for appropriate values of the mechanical anharmonicity strength the
steady-state mechanical squeezing and the ground-state cooling of the
mechanical resonator can be achieved. Moreover, we find that the presence of
the nonlinear gain medium can lead to the improvement of the mechanical
anharmonicity-induced cooling of the mechanical motion, as well as to the
mechanical squeezing beyond the standard quantum limit of 3 dB.Comment: 14 pages, 12 figure
Holographic superconductors with Weyl Corrections via gauge/gravity duality
In this paper, we analytically compute the basic parameters of the p-wave
holographic superconductors with Weyl geometrical corrections using the
matching method. The explicit correspondence between the critical temperature
and the dual charge density has been calculated as
and the dependence of the vacuum expectation value
for the dual condensate operator on the temperature has been found
analytically in the form . The critical exponent
is an universal quantity according to predictions of the mean field
theory and independent from the Weyl coupling . Our analytical results
confirm the numerical results and also agree on computations using by the
variational method.Comment: Published in "Int. J. Mod. Phys. A 28, 1350096 (2013)
Construction of a Holographic Superconductor in F(R) Gravity
We construct a toy model for holographic superconductor with non linear
Maxwell field in the frame of modified gravity. By probe the bulk background by
non linear Maxwell fields we show that superconductivity happens under a
specific critical temperature. The effect of the non linear Maxwell field and
non linear curvature corrections have been studied by analytical matching
methods. We conclude that the non linearity in Maxwell field and curvature
coupling make condensation harder.Comment: 20 pages, 18 figures, Preliminary versio
Condensation of the scalar field with Stuckelberg and Weyl Corrections in the background of a planar AdS-Schwarzschild black hole
We study analytical properties of the Stuckelberg holographic superconductors
with Weyl corrections. We obtain the minimum critical temperature as a function
of the mass of the scalar field . We show that in limit of the
, which is close to the
numerical estimate . Further we
show that the mass of the scalar field in bounded from below by the where . This lower bound is weaker and different
from the previous lower bound predicted by stability analysis. We show
that in the Breitenlohner-Freedman bound, the critical temperature remains
finite. Explicitly, we prove that here there is exist a linear relation between
and the chemical potential.Comment: Matched with published version,Replaced to remove text overlaps with
previous work by the same authors. arXiv admin note: substantial text overlap
with arXiv:1106.043
Realization of Holographic Entanglement Temperature for a Nearly-AdS boundary
Computing the holographic entanglement entropy proposed by Ryu-Takayanagi
shows that thermal energy near boundary region in gain maximum of the
temperature. The absolute maxima of temperature is . By simple physical investigations it has become
possible to predict a phase transition of first order at critical temperature
. As they predict a tail or root towards which the AdS space
ultimately tend, the boundary is considered thermalized. The Phase transitions
of this form have received striking theoretical and experimental verifications
so far.Comment: version accepted for publication in International Journal of
Theoretical Physics, 9 page
Reconstruction of f(T) and f(R) gravity according to (m,n)-type holographic dark energy
Motivated by earlier works on reconstruction of modified gravity models with
dark energy components, we extend them by considering a newly proposed model of
(m, n)- type of holographic dark energy for two models of modified gravity,
f(R) and f(T) theories, where R and T represent Ricci scalar and torsion scalar
respectively. Specifically we reconstruct the two later gravity models and
discuss their viability and cosmography. The obtained gravity models are ghost
free, compatible with local solar system tests and describe effective positive
gravitational constant.Comment: Published in: Canadian Journal of Physics, 10.1139/cjp-2012-043
Analytical holographic superconductors in Lifshitz topological black holes
We present the analytic Lifshitz solutions for a scalar field model minimally
coupled with the abelian gauge field in dimensions. We also consider the
presence of cosmological constant . The Lifshitz parameter
appearing in the solution plays the role of the Lorentz breaking parameter of
the model. We investigate the thermodynamical properties of the solutions and
discuss the energy issue. Furthermore, we study the hairy black hole solutions
in which the abelian gauge field breaks the symmetry near the horizon. In the
holographic picture, it is equivalent to a second order phase transition.
Explicitly we show that there exists a critical temperature which is a function
of the Lifshitz parameter . The system below the critical temperature
becomes superconductor, but the critical exponent of the model remains the same
of the usual holographic superconductors without the higher order gravitational
corrections, in agreement with Ginzburg-Landau theories.Comment: 27 pages, final version accepted in IJGMM
Evaporation phenomena in f(T) gravity
We formulate evaporation phenomena in a generic model of generalized
teleparallel gravity in Weitzenbock spacetime with diagonal and non-diagonal
tetrads basis. We also perform the perturbation analysis around the constant
torsion scalar solution named Nariai spacetime which is an exact solution of
field equations as the limiting case of the Schwarzschild-de Sitter and in the
limit where two back hole and their cosmological horizons coincide. By a
carefully analysis of the horizon perturbation equation, we show that
(anti)evaporation can not happen if we use a diagonal tetrad basis. This result
implies that a typical black hole in any generic form of generalized
teleparallel gravity is frozen in its initial state if we use the diagonal
tetrads. But in the case of non-diagonal tetrads the analysis is completely
different. By a suitable non trivial non-diagonal tetrad basis we investigate
the linear stability of the model under perturbations of the metric and torsion
simultaneously. We observe that in spite of the diagonal case, both evaporation
and anti evaporation can happen. The phenomena depend on the initial phase of
the horizon perturbation. In the first mode when we restrict ourselves to the
first lower modes the (anti)evaporation happens. So, in non-diagonal case the
physical phenomena is reasonable. This is an important advantage of using
non-diagonal tetrads instead of the diagonal ones. We also see that this is an
universal feature, completely independent from the form of the model.Comment: 16 pages, 2 figure
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