35,033 research outputs found
Gravitational Radiation from Cylindrical Naked Singularity
We construct an approximate solution which describes the gravitational
emission from a naked singularity formed by the gravitational collapse of a
cylindrical thick shell composed of dust. The assumed situation is that the
collapsing speed of the dust is very large. In this situation, the metric
variables are obtained approximately by a kind of linear perturbation analysis
in the background Morgan solution which describes the motion of cylindrical
null dust. The most important problem in this study is what boundary conditions
for metric and matter variables should be imposed at the naked singularity. We
find a boundary condition that all the metric and matter variables are
everywhere finite at least up to the first order approximation. This implies
that the spacetime singularity formed by this high-speed dust collapse is very
similar to that formed by the null dust and thus the gravitational emission
from a naked singularity formed by the cylindrical dust collapse can be gentle.Comment: 20 pages, 1 figur
Modulation of a Chirp Gravitational Wave from a Compact Binary due to Gravitational Lensing
A possible wave effect in the gravitational lensing phenomenon is discussed.
We consider the interference of two coherent gravitational waves of slightly
different frequencies from a compact binary, due to the gravitational lensing
by a galaxy halo. This system shows the modulation of the wave amplitude. The
lensing probability of such the phenomenon is of order 10^{-5} for a high-z
source, but it may be advantageous to the observation due to the magnification
of the amplitude.Comment: 3 pages, PRD in pres
Phase Field Model for Dynamics of Sweeping Interface
Motivated by the drying pattern experiment by Yamazaki and Mizuguchi[J. Phys.
Soc. Jpn. {\bf 69} (2000) 2387], we propose the dynamics of sweeping interface,
in which material distributed over a region is swept by a moving interface. A
model based on a phase field is constructed and results of numerical
simulations are presented for one and two dimensions. Relevance of the present
model to the drying experiment is discussed.Comment: 4 pages, 7 figure
Temperature-driven transition from the Wigner Crystal to the Bond-Charge-Density Wave in the Quasi-One-Dimensional Quarter-Filled band
It is known that within the interacting electron model Hamiltonian for the
one-dimensional 1/4-filled band, the singlet ground state is a Wigner crystal
only if the nearest neighbor electron-electron repulsion is larger than a
critical value. We show that this critical nearest neighbor Coulomb interaction
is different for each spin subspace, with the critical value decreasing with
increasing spin. As a consequence, with the lowering of temperature, there can
occur a transition from a Wigner crystal charge-ordered state to a spin-Peierls
state that is a Bond-Charge-Density Wave with charge occupancies different from
the Wigner crystal. This transition is possible because spin excitations from
the spin-Peierls state in the 1/4-filled band are necessarily accompanied by
changes in site charge densities. We apply our theory to the 1/4-filled band
quasi-one-dimensional organic charge-transfer solids in general and to 2:1
tetramethyltetrathiafulvalene (TMTTF) and tetramethyltetraselenafulvalene
(TMTSF) cationic salts in particular. We believe that many recent experiments
strongly indicate the Wigner crystal to Bond-Charge-Density Wave transition in
several members of the TMTTF family. We explain the occurrence of two different
antiferromagnetic phases but a single spin-Peierls state in the generic phase
diagram for the 2:1 cationic solids. The antiferromagnetic phases can have
either the Wigner crystal or the Bond-Charge-Spin-Density Wave charge
occupancies. The spin-Peierls state is always a Bond-Charge-Density Wave.Comment: 12 pages, 8 EPS figures. Longer version of previous manuscript.
Contains new numerical data as well as greatly expanded discussio
New criterion for direct black hole formation in rapidly rotating stellar collapse
We study gravitational collapse of rapidly rotating relativistic polytropes
of the adiabatic index and 2, in which the spin parameter where and are total angular momentum and
gravitational mass, in full general relativity.
First, analyzing initial distributions of the mass and the spin parameter
inside stars, we predict the final outcome after the collapse. Then, we perform
fully general relativistic simulations on assumption of axial and equatorial
symmetries and confirm our predictions. As a result of simulations, we find
that in contrast with the previous belief, even for stars with , the
collapse proceeds to form a seed black hole at central region, and the seed
black hole subsequently grows as the ambient fluids accrete onto it. We also
find that growth of angular momentum and mass of the seed black hole can be
approximately determined from the initial profiles of the density and the
specific angular momentum. We define an effective spin parameter at the central
region of the stars, , and propose a new criterion for black hole
formation as q_{c} \alt 1. Plausible reasons for the discrepancy between our
and previous results are clarified.Comment: submitted to PR
Theoretical analysis of the experiments on the double-spin-chain compound -- KCuCl
We have analyzed the experimental susceptibility data of KCuCl and found
that the data are well-explained by the double-spin-chain models with strong
antiferromagnetic dimerization. Large quantum Monte Carlo calculations were
performed for the first time in the spin systems with frustration. This was
made possible by removing the negative-sign problem with the use of the dimer
basis that has the spin-reversal symmetry. The numerical data agree with the
experimental data within 1% relative errors in the whole temperature region. We
also present a theoretical estimate for the dispersion relation and compare it
with the recent neutron-scattering experiment. Finally, the magnitude of each
interaction bond is predicted.Comment: 4 pages, REVTeX, 5 figures in eps-file
Phase diagram of the one dimensional Hubbard-Holstein Model at 1/2 and 1/4 filling
The Hubbard-Holstein model is one of the simplest to incorporate both
electron-electron and electron-phonon interactions. In one dimension at half
filling the Holstein electron-phonon coupling promotes onsite pairs of
electrons and a Peierls charge density wave while the Hubbard onsite Coulomb
repulsion U promotes antiferromagnetic correlations and a Mott insulating
state. Recent numerical studies have found a possible third intermediate phase
between Peierls and Mott states. From direct calculations of charge and spin
susceptibilities, we show that (i) As the electron-phonon coupling is
increased, first a spin gap opens, followed by the Peierls transition. Between
these two transitions the metallic intermediate phase has a spin gap, no charge
gap, and properties similar to the negative-U Hubbard model. (ii) The
transitions between Mott/intermediate and intermediate/Peierls states are of
the Kosterlitz-Thouless form. (iii) For larger U the two transitions merge at a
tritical point into a single first order Mott/Peierls transition. In addition
we show that an intermediate phase also occurs in the quarter-filled model.Comment: 10 pages, 10 eps figure
The last orbit of binary black holes
We have used our new technique for fully numerical evolutions of orbiting
black-hole binaries without excision to model the last orbit and merger of an
equal-mass black-hole system. We track the trajectories of the individual
apparent horizons and find that the binary completed approximately one and a
third orbits before forming a common horizon. Upon calculating the complete
gravitational radiation waveform, horizon mass, and spin, we find that the
binary radiated 3.2% of its mass and 24% of its angular momentum. The early
part of the waveform, after a relatively short initial burst of spurious
radiation, is oscillatory with increasing amplitude and frequency, as expected
from orbital motion. The waveform then transitions to a typical `plunge'
waveform; i.e. a rapid rise in amplitude followed by quasinormal ringing. The
plunge part of the waveform is remarkably similar to the waveform from the
previously studied `ISCO' configuration. We anticipate that the plunge
waveform, when starting from quasicircular orbits, has a generic shape that is
essentially independent of the initial separation of the binary.Comment: 5 pages, 5 figures, revtex
High Speed Dynamics of Collapsing Cylindrical Dust Fluid
We construct approximate solutions that will describe the last stage of
cylindrically symmetric gravitational collapse of dust fluid. Just before the
spacetime singularity formation, the speed of the dust fluid might be almost
equal to the speed of light by gravitational acceleration. Therefore the
analytic solution describing the dynamics of cylindrical null dust might be the
crudest approximate solution of the last stage of the gravitational collapse.
In this paper, we regard this null dust solution as a background and perform
`high-speed approximation' to know the gravitational collapse of ordinary
timelike dust fluid; the `deviation of the timelike
4-velocity vector field from null' is treated as a perturbation. In contrast
with the null dust approximation, our approximation scheme can describe the
generation of gravitational waves in the course of the cylindrically symmetric
dust collapse.Comment: 15 page
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