24 research outputs found
On the Evolution of Binary Neutron Stars
In this paper we investigate the evolution of binary neutron stars, namely,
their magnetic field, spin, and orbital evolution. The core of a neutron star
is considered to be a superfluid, superconductor type II. Flux expulsion of the
magnetic field out of the core of a single neutron star has been discussed by
previous authors. However, the evolution of the core magnetic field is
substantially different for a binary neutron star. While for a single neutron
star the fluxoids of the proton superconductor always move outward through the
core, in a binary neutron star in the accretion phase fluxoids move back into
the core. The subsequent increase of the core magnetic field results in the
increase of the surface magnetic field. We ask weather within the framework of
this model the formation of millisecond pulsars (MSPs) is possible. We show
that despite the increase of the core magnetic field, MSPs are formed in this
model. The evolution of the neutron star with various orbital periods, magnetic
fields, spin periods, and other parameters are numerically investigated. The
equation of state of the neutron star, initial orbital period of the binary,
and other parameters of the binary have substantial effects on the evolution of
period vs. magnetic field.Comment: 15 pages, 19 figures, 3 table
Production of black holes and string balls in a two-dimensional split-fermion model
We present cross-sections for the black hole and string ball production in
proton-proton collisions in a TeV-scale gravity model with split fermions in
two dimensions. The cross-section for black hole and string ball production in
the split-fermion model is smaller than in the non-split-fermion model. The
drop of the cross-section for the string ball production can be one to two
orders of magnitude with the increase of the width of the brane from to
15 . The cross-section for string ball production in
two-dimensional split fermion model reduces more in comparison to black holes.
Black holes are quite hard to be observed at the LHC. In fact, taking into
account the current experimental limits on the fundamental Planck scale, black
holes cannot be produced at the LHC. Cross-section for string ball production
depends significantly on string coupling constant, making it very model
dependent. We investigate the range of values of string coupling constant from
0.02 to 0.4. There has been no evidence for production of string balls at
TeV. A two-dimensional split fermion model with a extremely thick
brane can account for the absence of signature of string balls for a world with
the value of fundamental Planck scale even as low as 1 TeV.Comment: 28 pages 18 figure
Distorted Five-dimensional Electrically Charged Black Holes
We derive and study distorted, five-dimensional, electrically charged,
non-extremal black holes on the example of a static and "axisymmetric" black
hole distorted by external, electrically neutral matter.The solution satisfies
Einstein-Maxwell equations which admits an
isometry group. The inner horizon remains regular if the distortion fields are
finite and smooth at the outer horizon. There exists a certain duality
transformation between the inner and the outer horizon surfaces which links
surface gravity, electrostatic potential, and space-time curvature invariants
calculated at the black hole horizons. The product of the inner and outer
horizon areas depends only on the black hole's electric charge and the
geometric mean of the areas is the upper (lower) limit for the inner (outer)
horizon area. The horizon areas, electrostatic potential, and surface gravity
satisfy the Smarr formula. We formulated the zeroth and the first laws of
mechanics and thermodynamics of the distorted black hole and found a
correspondence between the global and local forms of the first law. To
illustrate the effect of distortion we consider the dipole-monopole and
quadrupole-quadrupole distortion fields. The relative change in the Kretschamnn
scalar due to the distortion is greater at the outer horizon than at the inner
one. Calculating the maximal proper time of free fall from the outer to the
inner horizons we show that the distortion can noticeably change the black hole
interior. The change depends on type and strength of distortion fields. In
particular, due to the types of distortion fields considered here the black
hole horizons can either come arbitrarily close to or move far from each other.Comment: 39 pages, 10 figure
Velocity Effects on an Accelerated Unruh-DeWitt Detector
We analyze the response of an Unruh-DeWitt detector moving along an unbounded
spatial trajectory in a two-dimensional spatial plane with constant independent
magnitudes of both the four-acceleration and of a timelike proper time
derivative of the four-accelration. In a Fermi-Walker frame moving with the
detector, the direction of the acceleration rotates at a constant rate around a
great circle. This is the motion of a charge in a uniform electric field when
in the frame of the charge there is both an electric and a magnetic field. We
compare the response of this detector to a detector moving with constant
velocity in a thermal bath of the corresponding temperature for
non-relativistic velocities, and in two regimes: ultraviolet and infrared. In
infrared regime, the detector in the Minkowski space-time moving along the
spatially two-dimensional trajectory should move with a higher speed to keep up
with the same excitation rate of the inertial detector in a thermal bath. In
ultraviolet regime, the dominant modification in the response of this detector
compared to the black body spectrum of Unruh radiation is the same as the
dominant modification perceived by a detector moving with constant velocity in
a thermal bath.Comment: (7 pages
Analysis of the Fisher solution
We study the -dimensional Fisher solution which represents a static,
spherically symmetric, asymptotically flat spacetime with a massless scalar
field. The solution has two parameters, the mass and the "scalar charge." The
Fisher solution has a naked curvature singularity which divides the spacetime
manifold into two disconnected parts. The part which is asymptotically flat we
call the {\em Fisher spacetime}, and another part we call the {\em Fisher
universe}. The Schwarzschild-Tangherlini (ST) solution and the Fisher solution
belong to the same theory and are dual to each other. The duality
transformation acting in the parameter space maps the exterior region of the ST
black hole into the Fisher spacetime which has a naked timelike singularity,
and interior region of the black hole into the Fisher universe, which is an
anisotropic expanding-contracting universe and which has two spacelike
singularities representing its "Big Bang" and "Big Crunch". The Big Bang
singularity and the singularity of the Fisher spacetime are {\em radially weak}
in the sense that a 1-dimensional object moving along a timelike radial
geodesic can arrive to the singularities intact. At the vicinity of the
singularity the Fisher spacetime of nonzero mass has a region where its
Misner-Sharp energy is negative. The Fisher universe has a marginally trapped
surface corresponding to the state of its maximal expansion in the angular
directions. These results and derived relations between geometric quantities of
the Fisher spacetime, the Fisher universe, and the ST black hole may suggest
that the massless scalar field transforms the black hole event horizon into the
naked radially weak disjoint singularities of the Fisher spacetime and the
Fisher universe which are "dual to the horizon."Comment: 19 pages, 16 figures; Minor changes in the tex
Hawking Radiation Energy and Entropy from a Bianchi-Smerlak Semiclassical Black Hole
Eugenio Bianchi and Matteo Smerlak have found a relationship between the
Hawking radiation energy and von Neumann entropy in a conformal field emitted
by a semiclassical two-dimensional black hole. We compare this relationship
with what might be expected for unitary evolution of a quantum black hole in
four and higher dimensions. If one neglects the expected increase in the
radiation entropy over the decrease in the black hole Bekenstein-Hawking A/4
entropy that arises from the scattering of the radiation by the barrier near
the black hole, the relation works very well, except near the peak of the
radiation von Neumann entropy and near the final evaporation. These
discrepancies are calculated and discussed as tiny differences between a
semiclassical treatment and a quantum gravity treatment.Comment: 20 pages, LaTeX, material added in pages 4-5 and 15-16 in response to
a referee's report, minor corrections adde
A Distorted Black Ring
We investigate how a static and neutral distribution of external matter
distorts a 5-dimensional static black ring. We obtain a general expression for
the distorted metric in terms of the background metric functions and the
distortion fields, and find a multipole expansion for the latter. We
demonstrate that the gravitational field of these external sources can be
adjusted to remove the conical singularity of the undistorted black ring
solution. We analyze properties of the distorted black ring for the specific
cases of dipole and quadrupole distortions.Comment: 16 pages and 7 figures. arXiv admin note: text overlap with
arXiv:hep-th/0110258 by other author
Distorted Local Shadows
We introduce the notion of a local shadow for a black hole and determine its
shape for the particular case of a distorted Schwarzschild black hole.
Considering the lowest-order even and odd multiple moments, we compute the
relation between the deformations of the shadow of a Schwarzschild black hole
and the distortion multiple moments. For the range of values of multiple
moments that we consider, the horizon is deformed much less than its
corresponding shadow, suggesting the horizon is more `rigid'. Quite
unexpectedly we find that a prolate distortion of the horizon gives rise to an
oblate distortion of the shadow, and vice-versa.Comment: 17 pages 18 figure
Double Images from a Single Black Hole
In the simulations of the multi-black holes and merging black holes a larger
primary image and a secondary smaller image which looks like an eyebrow and the
deformation of the shadows have been observed. However, this kind of
eyebrow-like structure was considered as unique feature of multi black hole
systems. In this paper, we illustrate the new result that in the case of
octupole distortions of a Schwarzschild black hole the local observer sees two
shadows or two images for this single black hole, i.e., also an eyebrow-like
structure. Presence of two images in our case is remarkable, as we have only
one black hole, however, the observer sees two dark images of this single black
hole.Comment: 26 pages, 17 figure
Properties of the distorted Kerr black hole
We investigate the properties of the ergoregion and the location of the
curvature singularities for the Kerr black hole distorted by the gravitational
field of external sources. The particular cases of quadrupole and octupole
distortion are studied in detail. We also investigate the scalar curvature
invariants of the horizon and compare their behaviour with the case of the
isolated Kerr black hole. In a certain region of the parameter space the
ergoregion consists of a compact region encompassing the horizon and a
disconnected part extending to infinity. The curvature singularities in the
domain of outer communication, when they exist, are always located on the
boundary of the ergoregion. We present arguments that they do not lie on the
compact ergosurface. For quadrupole distortion the compact ergoregion size is
negatively correlated with the horizon angular momentum when the external
sources are varied. For octupole distortion infinitely many ergoregion
configurations can exist for a certain horizon angular momentum. For some
special cases we can have and yet avoid the naked singularity.Comment: 51 pages, 26 figure