24,601 research outputs found
Neutrino Induced 4He Break-up Reaction -- Application of the Maximum Entropy Method in Calculating Nuclear Strength Function
The maximum entropy method is examined as a new tool for solving the
ill-posed inversion problem involved in the Lorentz integral transformation
(LIT) method. As an example, we apply the method to the spin-dipole strength
function of 4He. We show that the method can be successfully used for inversion
of LIT, provided the LIT function is available with a sufficient accuracy.Comment: 5 pages, 2 figures. Poster presented by TM at the International
Workshop on Neutrino-Nucleus Interaction in the Few-GeV Region (NuInt15),
Novenber 16-21 2015, Osaka, Japa
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
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
Horizon Pretracking
We introduce horizon pretracking as a method for analysing numerically
generated spacetimes of merging black holes. Pretracking consists of following
certain modified constant expansion surfaces during a simulation before a
common apparent horizon has formed. The tracked surfaces exist at all times,
and are defined so as to include the common apparent horizon if it exists. The
method provides a way for finding this common apparent horizon in an efficient
and reliable manner at the earliest possible time. We can distinguish inner and
outer horizons by examining the distortion of the surface. Properties of the
pretracking surface such as its expansion, location, shape, area, and angular
momentum can also be used to predict when a common apparent horizon will
appear, and its characteristics. The latter could also be used to feed back
into the simulation by adapting e.g. boundary or gauge conditions even before
the common apparent horizon has formed.Comment: 14 pages, 8 figures, minor change
Liquid phase epitaxy of GaAlAs on GaAs substrates with fine surface corrugations
Liquid phase epitaxy of GaAlAs was performed on GaAs fine surface corrugations. By optimizing the growth conditions, GaAlAs layers were grown successfully with only minimal meltback
Unitary coupled-channels model for three-mesons decays of heavy mesons
A unitary coupled-channels model is presented for investigating the decays of
heavy mesons and excited meson states into three light pseudoscalar mesons. The
model accounts for the three-mesons final state interactions in the decay
processes, as required by both the three-body and two-body unitarity
conditions. In the absence of the Z-diagram mechanisms that are necessary
consequences of the three-body unitarity, our decay amplitudes are reduced to a
form similar to those used in the so-called isobar-model analysis. We apply our
coupled-channels model to the three-pions decays of a1(1260), pi2(1670),
pi2(2100), and D0 mesons, and show that the Z-diagram mechanisms can contribute
to the calculated Dalitz plot distributions by as much as 30% in magnitudes in
the regions where f0(600), rho(770), and f2(1270) dominate the distributions.
Also, by fitting to the same Dalitz plot distributions, we demonstrate that the
decay amplitudes obtained with the unitary model and the isobar model can be
rather different, particularly in the phase that plays a crucial role in
extracting the CKM CP-violating phase from the data of B meson decays. Our
results indicate that the commonly used isobar model analysis must be extended
to account for the final state interactions required by the three-body
unitarity to reanalyze the three-mesons decays of heavy mesons, thereby
exploring hybrid or exotic mesons, and signatures of physics beyond the
standard model.Comment: 32 pages, 10 figures. Version to appear in PR
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
- …