50 research outputs found
Singularity Free Rainbow Universe
Isotropic quantum cosmological perfect fluid model is studied in the
formalism of Rainbow gravity. It is found that the only surviving matter degree
of freedom played the role of cosmic time. It is possible to find the wave
packet naturally with a suitable choice of the Rainbow functions which resulted
from the superposition of the wave functions of the
Schrdinger-Wheeler-deWitt equation. The many-worlds interpretation of
quantum mechanics is applied to investigate the behavior of the scale factor
and the behaviour is found to depend on the operator ordering. It is shown that
the model in the Rainbow framework naturally avoids singularity and a bouncing
non-singular universe is found.Comment: This essay received an honorable mention in the 2013 Essay
Competition of the Gravity Research Foundatio
Quantum Rainbow Cosmological Model With Perfect Fluid
Isotropic quantum cosmological perfect fluid model is studied in the
formalism of Rainbow gravity. It is found that the only surviving matter degree
of freedom played the role of cosmic time. With the suitable choice of the
Rainbow functions it is possible to find the wave packet naturally from the
superposition of the wave functions of the Schrdinger-Wheeler-deWitt
equation. The many-worlds interpretation of quantum mechanics is applied to
investigate the behavior of the scale factor and the behavior is found to
depend on the operator ordering. It is shown that the model in the Rainbow
framework may avoid singularity yielding a bouncing non-singular universe.Comment: To appear in Int. J. Mod. Phys. D. arXiv admin note: substantial text
overlap with arXiv:1305.370
f(R) in Holographic and Agegraphic Dark Energy Models and the Generalized Uncertainty Principle
We studied a unified approach with the holographic, new agegraphic and the
dark energy model to construct the form of which in general
responsible for the curvature driven explanation of the very early inflation
along with presently observed late time acceleration. We considered the
generalized uncertainty principle in our approach which incorporated the
corrections in the entropy area relation and thereby modified the energy
densities for the cosmological dark energy models considered. We found that
holographic and new agegraphic gravity models can behave like phantom or
quintessence models in the spatially flat FRW universe. We also found a
distinct term in the form of which goes as due to the
consideration of the GUP modified energy densities. Although the presence of
this term in the action can have its importance in explaining the early
inflationary scenario but Capozziello {\it et.al.} recently showed that leads to an accelerated expansion, {\it i.e.}, a negative
value for the deceleration parameter which fit well with SNeIa and WMAP
data.Comment: To appear in Advances in High Energy Physic
Electric Charges and Magnetic Monopoles in Gravity's Rainbow
In this work, we explore the possibility that quantum fluctuations induce an
electric or magnetic charge or both, in the context of Gravity's Rainbow. A
semi-classical approach is adopted, where the graviton one-loop contribution to
a classical energy in a background spacetime is computed through a variational
approach with Gaussian trial wave functionals. The energy density of the
graviton one-loop contribution, in this context, acts as a source for the
electric/magnetic charge. The ultraviolet (UV) divergences, which arise
analyzing this procedure, are kept under control with the help of an
appropriate choice of the Rainbow's functions. In this way we avoid the
introduction of any regularization/renormalization scheme. A comparison with
the observed data lead us to determine the size of the electron and of the
magnetic monopole which appear to be of Planckian size. Both results seem to be
of the same order for a Schwarzschild and a de Sitter background, respectively.
Estimates on the magnetic monopole size have been done with the help of the
Dirac quantization procedure. We find that the monopole radius is larger than
the electron radius. Even in this case the ratio between the electric and
magnetic monopole radius appears to be of the same order for both geometries.Comment: Updated to match with published version. RevTeX 4, 12 page
Black Hole Entropy and the Modified Uncertainty Principle: A heuristic analysis
Recently Ali et.al.(2009) proposed a Generalized Uncertainty Principle (or
GUP) with a linear term in momentum (accompanied by Plank length). Inspired by
this idea here we calculate the quantum corrected value of a Schwarzschild
black hole entropy and a Reissner-Nordstrom black hole with double horizon by
utilizing the proposed generalized uncertainty principle. We find that the
leading order correction goes with the square root of the horizon area
contributing positively. We also find that the prefactor of the logarithmic
contribution is negative and the value exactly matches with some earlier
existing calculations. With the Reissner-Nordstrom black hole we see that this
model independent procedure is not only valid for single horizon spacetime but
also valid for spacetimes with inner and outer horizons.Comment: 8 pages, accepted for publication in Physics Letters
Improved Universality in the Neutron Star Three-Hair Relations
No-hair like relations between the multipole moments of the exterior
gravitational field of neutron stars have recently been found to be
approximately independent of the star's internal structure. This approximate,
equation-of-state universality arises after one adimensionalizes the multipole
moments appropriately, which then begs the question of whether there are better
ways to adimensionalize the moments to obtain stronger universality. We here
investigate this question in detail by considering slowly-rotating neutron
stars both in the non-relativistic limit and in full General Relativity. We
find that there exist normalizations that lead to stronger equation-of-state
universality in the relations among the moment of inertia and the quadrupole,
octopole and hexadecapole moments of neutron stars. We determine the optimal
normalization that minimizes the equation-of-state dependence in these
relations. The results found here may have applications in the modeling of
X-ray pulses and atomic line profiles from millisecond pulsars with NICER and
LOFT.Comment: 11 pages, 10 figures, submitted to Phys. Rev.
Absence of an Effective Horizon for Black Holes in Gravity's Rainbow
We argue that the divergence in time for the asymptotic observer occurs
because of specifying the position of the Horizon beyond the Planck scale. In
fact, a similar divergence in time will also occur for an in-going observer in
Gravity's Rainbow, if we again specify the position of the Horizon beyond the
Planck scale. On the other hand, if we accept the occurrence of a minimum
measurable length scale associated with a universal invariant maximum energy
scale in Gravity's Rainbow, then the time taken by both the in-going and
asymptotic observers will be finite.Comment: 5 pages, revtex4, no figures, to appear in Europhysics Letter
Gravitational Collapse in Gravity's Rainbow
In this paper, we will analyze the gravitational collapse in the framework of
gravity's rainbow. We will demonstrate that the position of the horizon for a
particle inside the black hole depends on the energy of that particle. It will
also be observe that the position of the horizon for a particle falling
radially into the black hole also depends on its energy. Thus, it is possible
for a particle coming from outside to interact with a particle inside the
black, and take some information outside the black hole. This is because for
both these particles the position of horizon is different. So, even though the
particle from inside the black hole is in its own horizon, it is not in the
horizon of the particle coming from outside. Thus, we will demonstrate that in
gravity's rainbow information can get out of a black hole.Comment: accepted in Int. J. Geom. Methods Mod. Phy
Effects of the Modified Uncertainty Principle on the Inflation Parameters
In this Letter we study the effects of the Modified Uncertainty Principle as
proposed in [8] on the inflationary dynamics of the early universe in both
standard and Randall-Sundrum type II scenarios. We find that the quantum
gravitational effect increase the amplitude of density fluctuation, which is
oscillatory in nature, with an increase in the tensor-to-scalar ratio.Comment: new references adde