11 research outputs found

### Cosmic Censorship: The Role of Quantum Gravity

The cosmic censorship hypothesis introduced by Penrose thirty years ago is
still one of the most important open questions in {\it classical} general
relativity. In this essay we put forward the idea that cosmic censorship is
intrinsically a {\it quantum gravity} phenomena. To that end we construct a
gedanken experiment in which cosmic censorship is violated within the purely
{\it classical} framework of general relativity. We prove, however, that {\it
quantum} effects restore the validity of the conjecture. This suggests that
classical general relativity is inconsistent and that cosmic censorship might
be enforced only by a quantum theory of gravity.Comment: 7 pages. This essay received the Second Prize from the Gravity
Research Foundation 200

### Gravitational Effects of Quantum Fields in the Interior of a Cylindrical Black Hole

The gravitational back-reaction is calculated for the conformally invariant
scalar field within a black cosmic string interior with cosmological constant.
Using the perturbed metric, the gravitational effects of the quantum field are
calculated. It is found that the perturbations initially strengthen the
singularity. This effect is similar to the case of spherical symmetry (without
cosmological constant). This indicates that the behaviour of quantum effects
may be universal and not dependent on the geometry of the spacetime nor the
presence of a non-zero cosmological constant.Comment: 13 pages, 1 figure, uses AMS package. D.E. solution corrected. Some
qualitative results are change

### Entropy bound for a charged object from the Kerr-Newman black hole

We derive again the upper entropy bound for a charged object by employing
thermodynamics of the Kerr-Newman black hole linearised with respect to its
electric chargeComment: latex, 4 pages, no figures. In this version, the desired bound is
well obtained by varying correctly the entropy of the black hol

### Electrostatics in a Schwarzschild black hole pierced by a cosmic string

We explicitly determine the expression of the electrostatic potential
generated by a point charge at rest in the Schwarzschild black hole pierced by
a cosmic string. We can then calculate the electrostatic self-energy. From
this, we find again the upper entropy bound for a charged object by employing
thermodynamics of the black hole.Comment: Latex, 8 pages, 1 figure in late

### Self force on particle in orbit around a black hole

We study the self force acting on a scalar charge in uniform circular motion
around a Schwarzschild black hole. The analysis is based on a direct
calculation of the self force via mode decomposition, and on a regularization
procedure based on Ori's mode-sum regularization prescription. We find the four
self-force at arbitrary radii and angular velocities (both geodesic and
non-geodesic), in particular near the black hole, where general-relativistic
effects are strongest, and for fast motion. We find the radial component of the
self force to be repulsive or attractive, depending on the orbit.Comment: RevTeX, 4 pages, 4 Encapsulated PostScript figures. Submitted to
Phys. Rev. Let

### Black holes in which the electrostatic or scalar equation is solvable in closed form

We show that the method used in the Schwarzschild black hole for finding the
elementary solution of the electrostatic equation in closed form cannot extend
in higher dimensions. By contrast, we prove the existence of static,
spherically symmetric geometries with a non-degenerated horizon in which the
static scalar equation can be solved in closed form. We give the explicit
results in 6 dimensions. We determine moreover the expressions of the
electrostatic potential and of the static scalar field for a point source in
the extremal Reissner-Nordstrom black holes in higher dimensions.Comment: 20 pages, no figur

### Electrostatic boundary value problems in the Schwarzschild background

The electrostatic potential of any test charge distribution in Schwarzschild
space with boundary values is derived. We calculate the Green's function,
generalize the second Green's identity for p-forms and find the general
solution. Boundary value problems are solved. With a multipole expansion the
asymptotic property for the field of any charge distribution is derived. It is
shown that one produces a Reissner--Nordstrom black hole if one lowers a test
charge distribution slowly toward the horizon. The symmetry of the distribution
is not important. All the multipole moments fade away except the monopole. A
calculation of the gravitationally induced electrostatic self-force on a
pointlike test charge distribution held stationary outside the black hole is
presented.Comment: 18 pages, no figures, uses iopart.st

### Graviton Spectra in String Cosmology

We propose to uncover the signature of a stringy era in the primordial
Universe by searching for a prominent peak in the relic graviton spectrum. This
feature, which in our specific model terminates an $\omega^3$ increase and
initiates an $\omega^{-7}$ decrease, is induced during the so far overlooked
bounce of the scale factor between the collapsing deflationary era (or pre-Big
Bang) and the expanding inflationary era (or post-Big Bang). We evaluate both
analytically and numerically the frequency and the intensity of the peak and we
show that they may likely fall in the realm of the new generation of
interferometric detectors. The existence of a peak is at variance with
ordinarily monotonic (either increasing or decreasing) graviton spectra of
canonical cosmologies; its detection would therefore offer strong support to
string cosmology.Comment: 14 pages, RevTex source and 6 figures.p

### Self force on static charges in Schwarzschild spacetime

We study the self forces acting on static scalar and electric test charges in
the spacetime of a Schwarzschild black hole. The analysis is based on a direct,
local calculation of the self forces via mode decomposition, and on two
independent regularization procedures: A spatially-extended particle model
method, and on a mode-sum regularization prescription. In all cases we find
excellent agreement with the known exact results.Comment: 21 pages, 9 Encapsulated PostScript figures, submitted to Class.
Quantum Gra

### Self-force on a scalar point charge in the long throat

An analytic method is presented which allows for the computation of the
self-force for a static particle with a scalar charge in the region of an
ultrastatic spacetime which one can call the long throat. The method is based
on the approximate WKB solution of a radial mode equation for a scalar field.
This field is assumed to be massless, with a coupling $\xi$ to the scalar
curvature is satisfying the condition $\xi>1/8$.Comment: 11 pages, 1 figur