3,100 research outputs found
Vortices in Bose-Einstein Condensate Dark Matter
If dark matter in the galactic halo is composed of bosons that form a
Bose-Einstein condensate then it is likely that the rotation of the halo will
lead to the nucleation of vortices. After a review of the Gross-Pitaevskii
equation, the Thomas-Fermi approximation and vortices in general, we consider
vortices in detail. We find strong bounds for the boson mass, interaction
strength, the shape and quantity of vortices in the halo, the critical
rotational velocity for the nucleation of vortices and, in the Thomas-Fermi
regime, an exact solution for the mass density of a single, axisymmetric
vortex.Comment: 10 pages, 3 figures; minor corrections, references adde
The Effect of Sources on the Inner Horizon of Black Holes
Single pulse of null dust and colliding null dusts both transform a regular
horizon into a space-like singularity in the space of colliding waves. The
local isometry between such space-times and black holes extrapolates these
results to the realm of black holes. However, inclusion of particular scalar
fields instead of null dusts creates null singularities rather than space-like
ones on the inner horizons of black holes.Comment: Final version to appear in PR
From the self-force problem to the Radiation reaction formula
We review a recent theoretical progress in the so-called self-force problem
of a general relativistic two-body system. Although a two-body system in
Newtonian gravity is a very simple problem, some fundamental issues are
involved in relativistic gravity. Besides, because of recent projects for
gravitational wave detection, it comes to be possible to see those phenomena
directly via gravitational waves, and the self-force problem becomes one of
urgent and highly-motivated problems in general relativity. Roughly speaking,
there are two approaches to investigate this problem; the so-called
post-Newtonian approximation, and a black hole perturbation.
In this paper, we review a theoretical progress in the self-force problem
using a black hole perturbation. Although the self-force problem seems to be
just a problem to calculate a self-force, we discuss that the real problem is
to define a gauge invariant concept of a motion in a gauge dependent metric
perturbation.Comment: a special issue for Classical and Quantum Gravity, a review article
of Capra Ranch Meeting
Statistics of Largest Loops in a Random Walk
We report further findings on the size distribution of the largest neutral
segments in a sequence of N randomly charged monomers [D. Ertas and Y. Kantor,
Phys. Rev. E53, 846 (1996); cond-mat/9507005]. Upon mapping to one--dimensional
random walks (RWs), this corresponds to finding the probability distribution
for the size L of the largest segment that returns to its starting position in
an N--step RW. We primarily focus on the large N, \ell = L/N << 1 limit, which
exhibits an essential singularity. We establish analytical upper and lower
bounds on the probability distribution, and numerically probe the distribution
down to \ell \approx 0.04 (corresponding to probabilities as low as 10^{-15})
using a recursive Monte Carlo algorithm. We also investigate the possibility of
singularities at \ell=1/k for integer k.Comment: 5 pages and 4 eps figures, requires RevTeX, epsf and multicol.
Postscript file also available at
http://cmtw.harvard.edu/~deniz/publications.htm
Analytical approximation for the structure of differentially rotating barotropes
Approximate analytical formula for density distribution in differentially
rotating stars is derived. Any barotropic EOS and conservative rotation law can
be handled with use of this method for wide range of differential rotation
strength. Results are in good qualitative agreement with comparison to the
other methods. Some applications are suggested and possible improvements of the
formula are discussed.Comment: 10 pages, 13 figures, accepted for publication in Monthly Notice
Temperature dependent photoluminescence of organic semiconductors with varying backbone conformation
We present photoluminescence studies as a function of temperature from a
series of conjugated polymers and a conjugated molecule with distinctly
different backbone conformations. The organic materials investigated here are:
planar methylated ladder type poly para-phenylene, semi-planar polyfluorene,
and non-planar para hexaphenyl. In the longer-chain polymers the
photoluminescence transition energies blue shift with increasing temperatures.
The conjugated molecules, on the other hand, red shift their transition
energies with increasing temperatures. Empirical models that explain the
temperature dependence of the band gap energies in inorganic semiconductors can
be extended to explain the temperature dependence of the transition energies in
conjugated molecules.Comment: 8 pages, 9 figure
Orbital Ferromagnetism and Quantum Collapse in Stellar Plasmas
The possibility of quantum collapse and characteristics of nonlinear
localized excitations is examined in dense stars with Landau orbital
ferromagnetism in the framework of conventional quantum magnetohydrodynamics
(QMHD) model including Bohm force and spin-orbit polarization effects.
Employing the concepts of effective potential and Sagdeev pseudopotential, it
is confirmed that the quantum collapse and Landau orbital ferromagnetism
concepts are consistent with the magnetic field and mass-density range present
in some white dwarf stars. Furthermore, the value of ferromagnetic-field found
in this work is about the same order of magnitude as the values calculated
earlier. It is revealed that the magnetosonic nonlinear propagations can behave
much differently in the two distinct non-relativistic and relativistic
degeneracy regimes in a ferromagnetic dense astrophysical object. Current
findings should help to understand the origin of the most important mechanisms
such as gravitational collapse and the high magnetic field present in many
compact stars.Comment: To appear in journal Physics of Plasma
Solution of the Dirac equation in the rotating Bertotti-Robinson spacetime
The Dirac equation is solved in the rotating Bertotti-Robinson spacetime. The
set of equations representing the Dirac equation in the Newman-Penrose
formalism is decoupled into an axial and angular part. The axial equation,
which is independent of mass, is solved exactly in terms of hypergeometric
functions. The angular equation is considered both for massless (neutrino) and
massive spin-(1/2) particles. For the neutrinos, it is shown that the angular
equation admits an exact solution in terms of the confluent Heun equation. In
the existence of mass, the angular equation does not allow an analytical
solution, however, it is expressible as a set of first order differential
equations apt for numerical study.Comment: 17 pages, no figure. Appeared in JMP (May, 2008
Intermediate-mass-ratio-inspirals in the Einstein Telescope: I. Signal-to-noise ratio calculations
The Einstein Telescope (ET) is a proposed third generation ground-based
interferometer, for which the target is a sensitivity that is a factor of ten
better than Advanced LIGO and a frequency range that extends down to about 1Hz.
ET will provide opportunities to test Einstein's theory of relativity in the
strong field and will realize precision gravitational wave astronomy with a
thousandfold increase in the expected number of events over the advanced
ground-based detectors. A design study for ET is currently underway, so it is
timely to assess the science that could be done with such an instrument. This
paper is the first in a series that will carry out a detailed study of
intermediate-mass-ratio inspirals (IMRIs) for ET. In the context of ET, an IMRI
is the inspiral of a neutron star or stellar-mass black hole into an
intermediate mass black hole (IMBH). In this paper we focus on the development
of IMRI waveform models for circular and equatorial inspirals. We consider two
approximations for the waveforms, which both incorporate the inspiral, merger
and ringdown phases in a consistent way. One approximation, valid for IMBHs of
arbitrary spin, uses the transition model of Ori and Thorne [1] to describe the
merger, and this is then matched smoothly onto a ringdown waveform. The second
approximation uses the Effective One Body (EOB) approach to model the merger
phase of the waveform and is valid for non-spinning IMBHs. In this paper, we
use both waveform models to compute signal-to-noise ratios (SNRs) for IMRI
sources detectable by ET. At a redshift of z=1, we find typical SNRs for IMRI
systems with masses 1.4+100 solar masses, 10+100 solar masses, 1.4+500 solar
masses and 10+500 solar masses of about 10-25, 40-80, 3-15 and 10-60,
respectively. We also find that the two models make predictions for
non-spinning inspirals that are consistent to about ten percent.Comment: 27 pages, 9 figures, v3 has an updated reference for consistency with
accepted versio
Persistent junk solutions in time-domain modeling of extreme mass ratio binaries
In the context of metric perturbation theory for non-spinning black holes,
extreme mass ratio binary (EMRB) systems are described by distributionally
forced master wave equations. Numerical solution of a master wave equation as
an initial boundary value problem requires initial data. However, because the
correct initial data for generic-orbit systems is unknown, specification of
trivial initial data is a common choice, despite being inconsistent and
resulting in a solution which is initially discontinuous in time. As is well
known, this choice leads to a "burst" of junk radiation which eventually
propagates off the computational domain. We observe another unintended
consequence of trivial initial data: development of a persistent spurious
solution, here referred to as the Jost junk solution, which contaminates the
physical solution for long times. This work studies the influence of both types
of junk on metric perturbations, waveforms, and self-force measurements, and it
demonstrates that smooth modified source terms mollify the Jost solution and
reduce junk radiation. Our concluding section discusses the applicability of
these observations to other numerical schemes and techniques used to solve
distributionally forced master wave equations.Comment: Uses revtex4, 16 pages, 9 figures, 3 tables. Document reformatted and
modified based on referee's report. Commentary added which addresses the
possible presence of persistent junk solutions in other approaches for
solving master wave equation
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