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 $L=0$ to 15 $\text{TeV}^{-1}$. 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 $\sqrt{s}=8$ 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 $\mathbb{R}^1\times U(1)\times U(1)$ 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 $d$-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 $J^2/M^4 > 1$ and yet avoid the naked singularity.Comment: 51 pages, 26 figure