562 research outputs found
Critical collapse of a massive vector field
We perform numerical simulations of the critical gravitational collapse of a
massive vector field. The result is that there are two critical solutions. One
is equivalent to the Choptuik critical solution for a massless scalar field.
The other is periodic.Comment: 7 pages, 4 figure
An exact solution for 2+1 dimensional critical collapse
We find an exact solution in closed form for the critical collapse of a
scalar field with cosmological constant in 2+1 dimensions. This solution agrees
with the numerical simulation done by Pretorius and Choptuik of this system.Comment: 5 pages, 5 figures, Revtex. New comparison of analytic and numerical
solutions beyond the past light cone of the singularity added. Two new
references added. Error in equation (21) correcte
On the physical parametrization and magnetic analogs of the Emparan-Teo dihole solution
The Emparan-Teo non-extremal black dihole solution is reparametrized using
Komar quantities and the separation distance as arbitrary parameters. We show
how the potential can be calculated for the magnetic analogs of this
solution in the Einstein-Maxwell and Einstein-Maxwell-dilaton theories. We also
demonstrate that, similar to the extreme case, the external magnetic field can
remove the supporting strut in the non-extremal black dihole too.Comment: 9 pages, 1 figur
Homothetic Self-Similar Solutions of the Three-Dimensional Brans-Dicke Gravity
All homothetic self-similar solutions of the Brans-Dicke scalar field in
three-dimensional spacetime with circular symmetry are found in closed form.Comment: latex, five pages, without figur
Individualized Treatment of Criminal Offenders
For many years the nation\u27s criminologists and penologists have denounced the present system of treatment of criminal offenders as unrealistic and unproductive of desirable results. Dissatisfied with legislative tinkering at the peripheries of the problem, they have called for a sweeping re-examination of the basic procedures which appear untenable in the light of modern psychological knowledge.
In prior times the prime motive of society in its treatment of criminals was retribution; today it is still present, although in much reduced form. Deterrence from criminal acts and isolation of dangerous persons are present goals of criminal justice. Primarily, however, the aim is to rehabilitate offenders emotionally and vocationally for life in modern society. The period after sentencing, therefore, must be evaluated primarily on the basis of its success in the accomplishment of rehabilitation and, secondarily, deterrence of crime and isolation of those who cannot be rehabilitated.
The California Plan …
The Massachusetts Plan …
Action Taken in Other States …
Conclusion
Energy distribution of charged dilaton black holes
Chamorro and Virbhadra studied, using the energy-momentum complex of
Einstein, the energy distribution associated with static spherically symmetric
charged dilaton black holes for an arbitrary value of the coupling parameter
which controls the strength of the dilaton to the Maxwell field. We
study the same in Tolman's prescription and get the same result as obtained by
Chamorro and Virbhadra. The energy distribution of charged dilaton black holes
depends on the value of and the total energy is independent of this
parameter.Comment: 8 pages, RevTex, no figure
High velocity spikes in Gowdy spacetimes
We study the behavior of spiky features in Gowdy spacetimes. Spikes with
velocity initially high are, generally, driven to low velocity. Let n be any
integer greater than or equal to 1. If the initial velocity of an upward
pointing spike is between 4n-3 and 4n-1 the spike persists with final velocity
between 1 and 2, while if the initial velocity is between 4n-1 and 4n+1, the
spiky feature eventually disappears. For downward pointing spikes the analogous
rule is that spikes with initial velocity between 4n-4 and 4n-2 persist with
final velocity between 0 and 1, while spikes with initial velocity between 4n-2
and 4n eventually disappear.Comment: discussion of constraints added. Accepted for publication in Phys.
Rev.
Non-Stationary Dark Energy Around a Black Hole
Numerical simulations of the accretion of test scalar fields with
non-standard kinetic terms (of the k-essence type) onto a Schwarzschild black
hole are performed. We find a full dynamical solution for the spherical
accretion of a Dirac-Born-Infeld type scalar field. The simulations show that
the accretion eventually settles down to a well known stationary solution. This
particular analytical steady state solution maintains two separate horizons.
The standard horizon is for the usual particles propagating with the limiting
speed of light, while the other sonic horizon is for the k-essence
perturbations propagating with the speed of sound around this accreting
background. For the case where the k-essence perturbations propagate
superluminally, we show that one can send signals from within a black hole
during the approach to the stationary solution. We also find that a ghost
condensate model settles down to a stationary solution during the accretion
process.Comment: 8 pages, 10 figure
Pair creation of black holes joined by cosmic strings
We argue that production of charged black hole pairs joined by a cosmic
string in the presence of a magnetic field can be analyzed using the Ernst
metric. The effect of the cosmic string is to pull the black holes towards each
other, opposing to the background field. An estimation of the production rate
using the Euclidean action shows that the process is suppressed as compared to
the formation of black holes without strings.Comment: 7 pages, LaTeX. Minor typos corrected
Turbulence and Chaos in Anti-de-Sitter Gravity
Due to the AdS/CFT correspondence the question of instability of
Anti-de-Sitter spacetimes sits in the intersection of mathematical and
numerical relativity, string theory, field theory and condensed matter physics.
In this essay we revisit that important question emphasizing the power of
spectral methods and highlighting the effectiveness of standard techniques for
studying nonlinear dynamical systems. In particular we display explicitly how
the problem can be modeled as a system on nonlinearly coupled harmonic
oscillators. We highlight some of the many open questions that stem from this
result and point out that a full understanding will necessarily required the
interdisciplinary cooperation of various communities.Comment: 6 pages, 12 figures. Essay awarded honorable mention in the Gravity
Research Foundation essay competition 201
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