1,951 research outputs found
Quasinormal modes of a black hole with a cloud of strings in Einstein-Gauss-Bonnet gravity
The quasinormal modes for a scalar field in the background spacetime
corresponding to a black hole, with a cloud of strings, in
Einstein-Gauss-Bonnet gravity, and the tensor quasinormal modes corresponding
to perturbations in such spacetime, were both calculated using the WKB
approximation. In the obtained results we emphasize the role played by the
parameter associated with the string cloud, comparing them with the results
already obtained for the Boulware-Deser metric. We also study how the
Gauss-Bonnet correction to general relativity affects the results for the
quasinormal modes, comparing them with the same background in general
relativity.Comment: 15 pages, 7 figures; To appear in IJMP
Vacuum polarization by topological defects in de Sitter spacetime
In this paper we investigate the vacuum polarization effects associated with
a massive quantum scalar field in de Sitter spacetime in the presence of
gravitational topological defects. Specifically we calculate the vacuum
expectation value of the field square, . Because this investigation
has been developed in a pure de Sitter space, here we are mainly interested on
the effects induced by the presence of the defects.Comment: Talk presented at the 1st. Mediterranean Conference on Classical and
Quantum Gravity (MCCQG
Tsallis holographic dark energy in the Brans-Dicke cosmology
Using the Tsallis generalized entropy, holographic hypothesis and also
considering the Hubble horizon as the IR cutoff, we build a holographic model
for dark energy and study its cosmological consequences in the Brans-Dicke
framework. At first, we focus on a non-interacting universe, and thereinafter,
we study the results of considering a sign-changeable interaction between the
dark sectors of the cosmos. Our investigations show that, compared with the
flat case, the power and freedom of the model in describing the cosmic
evolution is significantly increased in the presence of the curvature. The
stability analysis also indicates that, independent of the universe curvature,
both the interacting and non-interacting cases are classically unstable. In
fact, both the classical stability criterion and an acceptable behavior for the
cosmos quantities, including the deceleration and density parameters as well as
the equation of state, are not simultaneously obtainable.Comment: Accepted version, Eur. Phys. J. C (2018
Global aspects of gravitomagnetism
We consider global properties of gravitomagnetism by investigating the
gravitomagnetic field of a rotating cosmic string. We show that although the
gravitomagnetic field produced by such a configuration of matter vanishes
locally, it can be detected globally. In this context we discuss the
gravitational analogue of the Aharonov-Bohm effect.Comment: 10 pages - Typeset using REVTE
Vacuum Polarization for a Massless Spin-1/2 Field in the Global Monopole Spacetime at Nonzero Temperature
In this paper we present the effects produced by the temperature in the
renormalized vacuum expectation value of the zero-zero component of the
energy-momentum tensor associated with massless left-handed spinor field in the
pointlike global monopole spacetime. In order to develop this calculation we
had to obtain the Euclidean thermal Green function in this background. Because
the expression obtained for the thermal energy density cannot be expressed in a
closed form, its explicit dependence on the temperature is not completely
evident. So, in order to obtain concrete information about its thermal
behavior, we develop a numerical analysis of our result in the high-temperature
limit for specific values of the parameter which codify the presence
of the monopole.Comment: 22 pages, LaTex format, 5 figure
Vacuum Polarization by a Magnetic Flux Tube at Finite Temperature in the Cosmic String Spacetime
In this paper we analyse the effect produced by the temperature in the vacuum
polarization associated with charged massless scalar field in the presence of
magnetic flux tube in the cosmic string spacetime. Three different
configurations of magnetic fields are taken into account: a homogeneous
field inside the tube, a field proportional to and a
cylindrical shell with -function. In these three cases, the axis of the
infinitely long tube of radius coincides with the cosmic string. Because
the complexity of this analysis in the region inside the tube, we consider the
thermal effect in the region outside. In order to develop this analysis, we
construct the thermal Green function associated with this system for the three
above mentioned situations considering points in the region outside the tube.
We explicitly calculate in the high-temperature limit, the thermal average of
the field square and the energy-momentum tensor.Comment: 16 pages, 1 figur
Self-energy and Self-force in the Space-time of a Thick Cosmic String
We calculate the self-energy and self-force for an electrically charged
particle at rest in the background of Gott-Hiscock cosmic string space-time. We
found the general expression for the self-energy which is expressed in terms of
the matrix of the scattering problem. The self-energy continuously falls
down outward from the string's center with maximum at the origin of the string.
The self-force is repulsive for an arbitrary position of the particle. It tends
to zero in the string's center and also far from the string and it has a
maximum value at the string's surface. The plots of the numerical calculations
of the self-energy and self-force are shown.Comment: 15 pages, 4 Postscript figures, ReVTe
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