4,106 research outputs found
Canonical Theory of 2+1 Gravity
Recently 2+1 dimensional gravity theory, especially has been
studied extensively. It was shown to be equivalent to the 2+1 Chern-Simon
theory and has been investigated to understand the black hole thermodynamics,
i.e. Hawking temperature and others. The purpose of this report is to
investigate the canonical formalism of the original 2+1 Einstein gravity theory
instead of the Chern-Simon theory. For the spherically symmetric space-time,
local conserved quantities(local mass and angular momentum) are introduced and
using them canonical quantum theory is defined. Constraints are imposed on
state vectors and solved analytically. The strategy to obtain the solution is
followed by our previous work.Comment: 6 pages, talk given at LLWI-2000: From Particles to Universe,
Alberta, 20-26 February 200
Models of Meson-Baryon Reactions in the Nucleon Resonance Region
It is shown that most of the models for analyzing meson-baryon reactions in
the nucleon resonance region can be derived from a Hamiltonian formulation of
the problem. An extension of the coupled-channel approach to include
channel is briefly described and some preliminary results for the
excitation are presented.Comment: Latex 13 pages; to appear in the Proceedings of Workshop on the
Physics of excited nucleons (NSTAR2004), Grenoble (France), March 24-27, 200
Weak localization and spin splitting in inversion layers on p-type InAs
We report on the magnetoconductivity of quasi two-dimensional electron
systems in inversion layers on p-type InAs single crystals. In low magnetic
fields pronounced features of weak localization and antilocalization are
observed. They are almost perfectly described by the theory of Iordanskii,
Lyanda-Geller and Pikus. This allows us to determine the spin splitting and the
Rashba parameter of the ground electric subband as a function of the electron
density.Comment: Accepted for publication in Phys. Rev. B, 4 page
Does a black hole rotate in Chern-Simons modified gravity?
Rotating black hole solutions in the (3+1)-dimensional Chern-Simons modified
gravity theory are discussed by taking account of perturbation around the
Schwarzschild solution. The zenith-angle dependence of a metric function
related to the frame-dragging effect is determined from a constraint equation
independently of a choice of the embedding coordinate. We find that at least
within the framework of the first-order perturbation method, the black hole
cannot rotate for finite black hole mass if the embedding coordinate is taken
to be a timelike vector. However, the rotation can be permitted in the limit of
(where is the black hole mass and is the radius). For a
spacelike vector, the rotation can also be permitted for any value of the black
hole mass.Comment: 4 pages, Accepted for publication in Phys. Rev.
Global well-posedness of the Kirchhoff equation and Kirchhoff systems
This article is devoted to review the known results on global well-posedness
for the Cauchy problem to the Kirchhoff equation and Kirchhoff systems with
small data. Similar results will be obtained for the initial-boundary value
problems in exterior domains with compact boundary. Also, the known results on
large data problems will be reviewed together with open problems.Comment: arXiv admin note: text overlap with arXiv:1211.300
Nitrogen Fixation Mutants of the Actinobacterium Frankia Casuarinae CcI3
Frankia is a representative genus of nitrogen-fixing (N2-fixing) actinobacteria; however, the molecular mechanisms underlying various phenomena such as the differentiation of a N2 fixation-specific structure (vesicle) and the regulation of N2 fixation (nif) genes, have yet to be elucidated in detail. In the present study, we screened hyphal fragments of Frankia casuarinae that were mutagenized by 1-methyl-3-nitro-1-nitrosoguanidine or gamma rays, and isolated 49 candidate N2 fixation mutants. Twelve of these mutants were selected for further study, and their abilities to grow in NH3-deficient (N-) liquid media and their rates of acetylene reduction activities were evaluated. Eleven mutant strains were confirmed to lack the ability to fix N2. Five mutant strains formed significantly reduced numbers of vesicles, while some failed to form large mature vesicles. These vesicle mutants also exhibited an aberrant hyphal morphology, suggesting a relationship between vesicle differentiation and hyphal branching. Ten mutants showed significant reductions in the expression of nifE, nifH, and nifV genes under N- conditions. The genome sequencing of eight mutants identified 20 to 400 mutations. Although mutant strains N3H4 and N6F4 shared a large number of mutations (108), most were unique to each strain. Mutant strain N7C9 had 3 mutations in the nifD and nifH genes that may result in the inability to fix N2. The other mutant strains did not have any mutations in any known N2 fixation-related genes, indicating that they are novel N2 fixation mutants
True polar wander driven by late-stage volcanism and the distribution of paleopolar deposits on Mars
The areal centroids of the youngest polar deposits on Mars are offset from
those of adjacent paleopolar deposits by 5-10 degrees. We test the hypothesis
that the offset is the result of true polar wander (TPW), the motion of the
solid surface with respect to the spin axis, caused by a mass redistribution
within or on the surface of Mars. In particular, we consider TPW driven by
late-stage volcanism during the late Hesperian to Amazonian. There is
observational and qualitative support for this hypothesis: in both North and
South, observed offsets lie close to a great circle 90 degrees from Tharsis, as
expected for polar wander after Tharsis formed. We calculate the magnitude and
direction of TPW produced by mapped late-stage lavas for a range of
lithospheric thicknesses, lava thicknesses, eruption histories, and prior polar
wander events. If Tharsis formed close to the equator, the stabilizing effect
of a fossil rotational bulge located close to the equator leads to predicted
TPW of <2 degrees, too small to account for observed offsets. If, however,
Tharsis formed far from the equator, late-stage TPW driven by low-latitude,
late-stage volcanism would be 6-33 degrees, similar to that inferred from the
location of paleopolar deposits. 4.4+/-1.3x10^19 kg of young erupted lava can
account for the offset of the Dorsa Argentea Formation from the present-day
south rotation pole. This mass is consistent with prior mapping-based estimates
and would imply a mass release of CO2 by volcanic degassing similar to that in
the atmosphere at the present time. The South Polar Layered Deposits are offset
from the spin axis in the opposite sense to the other paleopolar deposits. This
can be explained by an additional contribution from a plume beneath Elysium. We
conclude with a list of observational tests of the TPW hypothesis.Comment: Accepted by Earth and Planetary Science Letters. 3 tables, 8 figure
Dynamical Coupled-Channels Effects on Pion Photoproduction
The electromagnetic pion production reactions are investigated within the
dynamical coupled-channels model developed in {\bf Physics Reports, 439, 193
(2007)}. The meson-baryon channels included in this study are , , , and the , and resonant components
of the channel. With the hadronic parameters of the model determined
in a recent study of scattering, we show that the pion photoproduction
data up to the second resonance region can be described to a very large extent
by only adjusting the bare helicity amplitudes, while the
non-resonant electromagnetic couplings are taken from previous works. It is
found that the coupled-channels effects can contribute about 10 - 20 % of the
production cross sections in the (1232) resonance region, and can
drastically change the magnitude and shape of the cross sections in the second
resonance region. The importance of the off-shell effects in a dynamical
approach is also demonstrated. The meson cloud effects as well as the
coupled-channels contributions to the form factors are found
to be mainly in the low region. For the magnetic M1
(1232) form factor, the results are close to that of the Sato-Lee Model.
Necessary improvements to the model and future developments are discussed.Comment: Corrected version. 14 pages, 10 figure
Double and single pion photoproduction within a dynamical coupled-channels model
Within a dynamical coupled-channels model which has already been fixed from
analyzing the data of the pi N -> pi N and gamma N -> pi N reactions, we
present the predicted double pion photoproduction cross sections up to the
second resonance region, W< 1.7 GeV. The roles played by the different
mechanisms within our model in determining both the single and double pion
photoproduction reactions are analyzed, focusing on the effects due to the
direct gamma N -> pi pi N mechanism, the interplay between the resonant and
non-resonant amplitudes, and the coupled-channels effects. The model parameters
which can be determined most effectively in the combined studies of both the
single and double pion photoproduction data are identified for future studies.Comment: Version to appear in PRC. 16 pages, 13 figure
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