21 research outputs found
Hawking temperature of rotating charged black strings from tunneling
Thermal radiations from spherically symmetric black holes have been studied
from the point of view of quantum tunneling. In this paper we extend this
approach to study radiation of fermions from charged and rotating black
strings. Using WKB approximation and Hamilton-Jacobi method we work out the
tunneling probabilities of incoming and outgoing fermions and find the correct
Hawking temperature for these objects. We show that in appropriate limits the
results reduce to those for the uncharged and non-rotating black strings
Nariai, Bertotti-Robinson and anti-Nariai solutions in higher dimensions
We find all the higher dimensional solutions of the Einstein-Maxwell theory
that are the topological product of two manifolds of constant curvature. These
solutions include the higher dimensional Nariai, Bertotti-Robinson and
anti-Nariai solutions, and the anti-de Sitter Bertotti-Robinson solutions with
toroidal and hyperbolic topology (Plebanski-Hacyan solutions). We give explicit
results for any dimension D>3. These solutions are generated from the
appropriate extremal limits of the higher dimensional near-extreme black holes
in a de Sitter, and anti-de Sitter backgrounds. Thus, we also find the mass and
the charge parameters of the higher dimensional extreme black holes as a
function of the radius of the degenerate horizon.Comment: 10 pages, 11 figures, RevTeX4. References added. Published versio
Hairy rotating black string in the Einstein-Maxwell-Higgs system
We show numerically that the Abelian Higgs field equations in the background
of a four-dimensional rotating charged black string have vortex solutions.
These solutions which have axial symmetry show that the rotating black string
can support the Abelian Higgs field as hair. We find that one encounters with
an electric field coupled to the Higgs scalar field for the case of rotating
black string. This electric field is due to an electric charge per unit length,
which increases as the rotation parameter becomes larger. We also find that the
vortex thickness decreases as the rotation parameter grows up. Finally we
consider the self-gravity of the Abelian Higgs field and show that the effect
of the vortex is to induce a deficit angle in the metric under consideration
which decreases as the rotation parameter increases.Comment: 16 pages, 8 figures, references added, some minor corrections don
The extremal limits of the C-metric: Nariai, Bertotti-Robinson and anti-Nariai C-metrics
In two previous papers we have analyzed the C-metric in a background with a
cosmological constant, namely the de Sitter (dS) C-metric, and the anti-de
Sitter (AdS) C-metric, following the work of Kinnersley and Walker for the flat
C-metric. These exact solutions describe a pair of accelerated black holes in
the flat or cosmological constant background, with the acceleration A being
provided by a strut in-between that pushes away the two black holes. In this
paper we analyze the extremal limits of the C-metric in a background with
generic cosmological constant. We follow a procedure first introduced by
Ginsparg and Perry in which the Nariai solution, a spacetime which is the
direct topological product of the 2-dimensional dS and a 2-sphere, is generated
from the four-dimensional dS-Schwarzschild solution by taking an appropriate
limit, where the black hole event horizon approaches the cosmological horizon.
Similarly, one can generate the Bertotti-Robinson metric from the
Reissner-Nordstrom metric by taking the limit of the Cauchy horizon going into
the event horizon of the black hole, as well as the anti-Nariai by taking an
appropriate solution and limit. Using these methods we generate the C-metric
counterparts of the Nariai, Bertotti-Robinson and anti-Nariai solutions, among
others. One expects that the solutions found in this paper are unstable and
decay into a slightly non-extreme black hole pair accelerated by a strut or by
strings. Moreover, the Euclidean version of these solutions mediate the quantum
process of black hole pair creation, that accompanies the decay of the dS and
AdS spaces
Horizonless Rotating Solutions in -dimensional Einstein-Maxwell Gravity
We introduce two classes of rotating solutions of Einstein-Maxwell gravity in
dimensions which are asymptotically anti-de Sitter type. They have no
curvature singularity and no horizons. The first class of solutions, which has
a conic singularity yields a spacetime with a longitudinal magnetic field and
rotation parameters. We show that when one or more of the rotation
parameters are non zero, the spinning brane has a net electric charge that is
proportional to the magnitude of the rotation parameters. The second class of
solutions yields a spacetime with an angular magnetic field and
boost parameters. We find that the net electric charge of these traveling
branes with one or more nonzero boost parameters is proportional to the
magnitude of the velocity of the brane. We also use the counterterm method
inspired by AdS/CFT correspondence and calculate the conserved quantities of
the solutions. We show that the logarithmic divergencies associated to the Weyl
anomalies and matter field are zero, and the divergence of the action can
be removed by the counterterm method.Comment: 14 pages, references added, Sec. II amended, an appendix added. The
version to appear in Phys. Rev.
Four-dimensional anti-de Sitter black holes from a three-dimensional perspective: Full complexity
The dimensional reduction of black hole solutions in four-dimensional (4D)
general relativity is performed and new 3D black hole solutions are obtained.
Considering a 4D spacetime with one spacelike Killing vector, it is possible to
split the Einstein-Hilbert-Maxwell action with a cosmological term in terms of
3D quantities. Definitions of quasilocal mass and charges in 3D spacetimes are
reviewed. The analysis is then particularized to the toroidal charged rotating
anti-de Sitter black hole. The reinterpretation of the fields and charges in
terms of a three-dimensional point of view is given in each case, and the
causal structure analyzed.Comment: 26 pages, 1 figure, Uses revtex
Thin-shell wormholes with a generalized Chaplygin gas in Einstein-Born-Infeld theory
We construct spherically symmetric thin-shell wormholes supported by a
generalized Chaplygin gas in Born-Infeld electrodynamics coupled to Einstein
gravity, and we analyze their stability under radial perturbations. For
different values of the Born-Infeld parameter and the charge, we compare the
results with those obtained in a previous work for Maxwell electrodynamics. The
stability region in the parameter space reduces and then disappears as the
value of the Born-Infeld parameter is modified in the sense of a larger
departure from Maxwell theory.Comment: 9 pages, 6 figures; v2: improved versio
Thin-shell wormholes from black holes with dilaton and monopole fields
We provide a new type of thin-shell wormhole from the black holes with
dilaton and monopole fields. The dilaton and monopole that built the black
holes may supply fuel to construct the wormholes. Several characteristics of
this thin-shell wormhole have been discussed. Finally, we discuss the stability
of the thin-shell wormholes with a "phantom-like" equation of state for the
exotic matter at the throat.Comment: 6 pages and 3 figures, some typos are corrected and accepted in
Int.J.Theor.Phy
Stability of Non-asymptotically flat thin-shell wormholes in generalized dilaton-axion gravity
We construct a new type of thin-shell wormhole for non-asymptotically flat
charged black holes in generalized dilaton-axion gravity inspired by low-energy
string theory using cut-and-paste technique. We have shown that this thin shell
wormhole is stable. The most striking feature of our model is that the total
amount of exotic matter needed to support the wormhole can be reduced as
desired with the suitable choice of the value of a parameter. Various other
aspects of thin-shell wormhole are also analyzed.Comment: 15 pages and 11 figures. Minor revisions have been done. Accepted in
Int.J.Theor.Phy
Wearable Biomonitoring Platform for the Assessment of Stress and its Impact on Cognitive Performance of Firefighters: An Experimental Study
Background: Stress is a complex process with an impact on health and performance. The use of wearable sensor-based monitoring systems offers interesting opportunities for advanced health care solutions for stress analysis. Considering the stressful nature of firefighting and its importance for the community’s safety, this study was conducted for firefighters. Objectives: A biomonitoring platform was designed, integrating different biomedical systems to enable the acquisition of real time Electrocardiogram (ECG), computation of linear Heart Rate Variability (HRV) features and collection of perceived stress levels. This platform was tested using an experimental protocol, designed to understand the effect of stress on firefighter’s cognitive performance, and whether this effect is related to the autonomic response to stress. Method: The Trier Social Stress Test (TSST) was used as a testing platform along with a 2-Choice Reaction Time Task. Linear HRV features from the participants were acquired using an wearable ECG. Self-reports were used to assess perceived stress levels. Results: The TSST produced significant changes in some HRV parameters (AVNN, SDNN and LF/HF) and subjective measures of stress, which recovered after the stress task. Although these short-term changes in HRV showed a tendency to normalize, an impairment on cognitive performance was found after performing the stress event. Conclusion: Current findings suggested that stress compromised cognitive performance and caused a measurable change in autonomic balance. Our wearable biomonitoring platform proved to be a useful tool for stress assessment and quantification. Future studies will implement this biomonitoring platform for the analysis of stress in ecological settings