5,852 research outputs found
Structures in the microwave background radiation
We compare the actual WMAP maps with artificial, purely statistical maps of
the same harmonic content to argue that there are, with confidence level 99.7
%, ring-type structures in the observed cosmic microwave background.Comment: 4 pages, 2 figure
Alternative experimental evidence for chiral restoration in excited baryons
Given existing empirical spectral patterns of excited hadrons it has been
suggested that chiral symmetry is approximately restored in excited hadrons at
zero temperature/density (effective symmetry restoration). If correct, this
implies that mass generation mechanisms and physics in excited hadrons is very
different as compared to the lowest states. One needs an alternative and
independent experimental information to confirm this conjecture. Using very
general chiral symmetry arguments it is shown that strict chiral restoration in
a given excited nucleon forbids its decay into the N \pi channel. Hence those
excited nucleons which are assumed from the spectroscopic patterns to be in
approximate chiral multiplets must only "weakly" decay into the N \pi channel,
(f_{N^*N\pi}/f_{NN\pi})^2 << 1. However, those baryons which have no chiral
partner must decay strongly with a decay constant comparable with f_{NN\pi}.
Decay constants can be extracted from the existing decay widths and branching
ratios. It turnes out that for all those well established excited nucleons
which can be classified into chiral doublets N_+(1440) - N_-(1535), N_+(1710) -
N_-(1650), N_+(1720) - N_-(1700), N_+(1680) - N_-(1675), N_+(2220) - N_-(2250),
N_+(?) - N_-(2190), N_+(?) - N_-(2600), the ratio is (f_{N^*N\pi}/f_{NN\pi})^2
~ 0.1 or much smaller for the high-spin states. In contrast, the only well
established excited nucleon for which the chiral partner cannot be identified
from the spectroscopic data, N(1520), has a decay constant into the N\pi
channel that is comparable with f_{NN\pi}. This gives an independent
experimental verification of the chiral symmetry restoration scenario.Comment: 4 pp. A new footnote with an alternative proof of impossibility of
parity doublet decay into pi + N is added. To appear in Phys. Rev. Let
The use of computer-generated color graphic images for transient thermal analysis
Color computer graphics techniques were investigated as a means of rapidly scanning and interpreting large sets of transient heating data. The data presented were generated to support the conceptual design of a heat-sink thermal protection system (TPS) for a hypersonic research airplane. Color-coded vector and raster displays of the numerical geometry used in the heating calculations were employed to analyze skin thicknesses and surface temperatures of the heat-sink TPS under a variety of trajectory flight profiles. Both vector and raster displays proved to be effective means for rapidly identifying heat-sink mass concentrations, regions of high heating, and potentially adverse thermal gradients. The color-coded (raster) surface displays are a very efficient means for displaying surface-temperature and heating histories, and thereby the more stringent design requirements can quickly be identified. The related hardware and software developments required to implement both the vector and the raster displays for this application are also discussed
Isospin breaking in the pion-nucleon scattering lengths
We analyze isospin breaking through quark mass differences and virtual photons in the pion-nucleon scattering lengths in all physical channels in the framework of covariant baryon chiral perturbation theory (C) 2009 Elsevier B.V. All rights reserved
Multi-Magnon Scattering in the Ferromagnetic XXX-Model with Inhomogeneities
We determine the transition amplitude for multi-magnon scattering induced
through an inhomogeneous distribution of the coupling constant in the
ferromagnetic XXX-model. The two and three particle amplitudes are explicitely
calculated at small momenta. This suggests a rather plausible conjecture also
for a formula of the general n-particle amplitude.Comment: 21 pages, latex, no figure
The Nucleon Anapole Moment and Parity-Violating ep Scattering
Parity-violating (PV) interactions among quarks in the nucleon induce a PV
coupling, or anapole moment (AM). We compute electroweak
gauge-independent contributions to the AM through {\cal O}(1/\lamchis) in
chiral perturbation theory. We estimate short-distance PV effects using
resonance saturation. The AM contributions to PV electron-proton scattering
slightly enhance the axial vector radiative corrections, R_A^p, over the scale
implied by the Standard Model when weak quark-quark interactions are neglected.
We estimate the theoretical uncertainty associated with the AM contributions to
R_A^p to be large, and discuss the implications for the interpretation PV of ep
scattering.Comment: RevTex 29 pages + 8 PS figures, references and discussions added, to
appear in Phys. Rev.
The Medio Creek Site (41BX1421): National Register Test Excavations, Bexar County Texas
During April 2001, the Center for Archaeological Research of The University of Texas at San Antonio conducted National Register of Historic Places eligibility testing for archeological site 41BX1421, located in southwest Bexar County, Texas, under contract with the Texas Department of Transportation. The investigations were conducted under Texas Antiquities Permit Number 2569. The Phase II testing fieldwork consisted of excavation of five test units across the site to investigate cultural deposits encountered during the previous survey phase. A single sheet midden consisting of burned limestone cobbles was encountered across the majority of the site. In concert with the archeological field investigations, the following special analyses and studies were performed to aid the determination of site integrity and eligibility: radiocarbon, lithic, aboriginal ceramic, vertebrate faunal. and magnetic sediment susceptibility. The synthesis of these analyses has provided adequate data to determine 41BX1421 ineligible for the National Register of Historic Places. It is therefore recommended that the Loop 1604 improvements proceed without further cultural resources investigations
High-pressure spin shifts in the pseudogap regime of superconducting YBa2Cu4O8 as revealed by 17O NMR
A new NMR anvil cell design is used for measuring the influence of high
pressure on the electronic properties of the high-temperature superconductor
YBaCuO above the superconducting transition temperature . It is found that pressure increases the spin shift at all temperatures in
such a way that the pseudo-gap feature has almost disappeared at 63 kbar. This
change of the temperature dependent spin susceptibility can be explained by a
pressure induced proportional decrease (factor of two) of a temperature
dependent component, and an increase (factor of 9) of a temperature independent
component, contrary to the effects of increasing doping. The results
demonstrate that one can use anvil cell NMR to investigate the tuning of the
electronic properties of correlated electronic materials with pressure.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev.
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