13,279 research outputs found
The Kaon B-parameter from Quenched Domain-Wall QCD
We present numerical results for the kaon B-parameter, B_K, determined in the
quenched approximation of lattice QCD. Our simulations are performed using
domain-wall fermions and the renormalization group improved, DBW2 gauge action
which combine to give quarks with good chiral symmetry at finite lattice
spacing. Operators are renormalized non-perturbatively using the RI/MOM scheme.
We study scaling by performing the simulation on two different lattices with
a^{-1} = 1.982(30) and 2.914(54) GeV. We combine this quenched scaling study
with an earlier calculation of B_K using two flavors of dynamical, domain-wall
quarks at a single lattice spacing to obtain
B_K(MS,NDR,mu=2GeV)=0.563(21)(39)(30), were the first error is statistical, the
second systematic (without quenching errors) and the third estimates the error
due to quenching.Comment: 77 pages, 44 figures, to be published in Phys. Rev.
A Case History of Liquefaction Flow Failures in Mountains Mine Waste Dumps
Over the past 25 years there have been a large number of flowslides in Rocky Mountain coal mine waste dumps located in British Columbia, Canada. The flowslides occurred rapidly and displayed surprisingly long distance of runout up to 2 km. Detailed field, laboratory studies, and analyses indicate that static collapse of saturated or nearly saturated sandy gravel layers within the dumps are responsible for the initial failure and ensuing flow failures. In addition to field and laboratory studies, finite element analyses were carried out on three case histories. The analysis results indicated that the flow like liquefaction failures of these waste dumps can be triggered by gradually raising of perched water tables contained within thin layers or poorly draining waste material in these slopes. This paper reviews the site condition and failure pattern observed in the mountainous mine waste dumps and investigates the mechanism of static liquefaction failure by finite element methods
Radio observations of the double-relic galaxy cluster Abell 1240
We present LOFAR 120 â 168 MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the GMRT 595 â 629 MHz and VLA 2 â 4 GHz data, we characterised the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration (DSA), we obtain shock Mach numbers of M = 2.4 and 2.3 for the northern and southern shocks, respectively. For M âČ 3 shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high (> 10 per cent) particle acceleration efficiency required. However, for M âł 4 shocks the required efficiency is âł 1% and âł 0.5%, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to â„ 53 ± 3° and â„ 39 ± 5° for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics (âŒ1.8 Mpc) our upper limit on the power is P1.4 GHz = (1.4 ± 0.6) Ă 1023 W Hzâ1 which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous
First Detection of HCO Absorption in the Magellanic System
We present the first detection of HCO absorption in the Magellanic
System. Using the Australia Telescope Compact Array (ATCA), we observed 9
extragalactic radio continuum sources behind the Magellanic System and detected
HCO absorption towards one source located behind the leading edge of the
Magellanic Bridge. The detection is located at LSR velocity of , with a full width at half maximum of and optical depth of .
Although there is abundant neutral hydrogen (HI) surrounding the sightline in
position-velocity space, at the exact location of the absorber the HI column
density is low, , and there is little evidence for dust
or CO emission from Planck observations. While the origin and survival of
molecules in such a diffuse environment remains unclear, dynamical events such
as HI flows and cloud collisions in this interacting system likely play an
important role.Comment: Accepted for publication in ApJ. 6 pages, 2 figures, 2 table
Minijet corrections to Higgs production
We study higher order corrections to Higgs production with an associated jet
at SSC energies, using the resummation of the leading logarithmic contributions
to multiple gluon emissions due to Lipatov and collaborators. We find a
considerable enhancement of Higgs production at large transverse momenta.Comment: 15 page
Assessment of energy and nutrient content of a recipe food box for schoolchildren âNutrition in a BRITE Boxâ
Auxiliary field approach to dilute Bose gases with tunable interactions
We rewrite the Lagrangian for a dilute Bose gas in terms of auxiliary fields
related to the normal and anomalous condensate densities. We derive the loop
expansion of the effective action in the composite-field propagators. The
lowest-order auxiliary field (LOAF) theory is a conserving mean-field
approximation consistent with the Goldstone theorem without some of the
difficulties plaguing approximations such as the Hartree and Popov
approximations. LOAF predicts a second-order phase transition. We give a set of
Feynman rules for improving results to any order in the loop expansion in terms
of composite-field propagators. We compare results of the LOAF approximation
with those derived using the Popov approximation. LOAF allows us to explore the
critical regime for all values of the coupling constant and we determine
various parameters in the unitarity limit.Comment: 16 pages, 7 figure
Inelastic contribution of the resistivity in the hidden order in URu2Si2
In the hidden order of URu2Si2 the resistivity at very low temperature shows
no T^2 behavior above the transition to superconductivity. However, when
entering the antiferromagnetic phase, the Fermi liquid behavior is recovered.
We discuss the change of the inelastic term when entering the AF phase with
pressure considering the temperature dependence of the Grueneisen parameter at
ambient pressure and the influence of superconductivity by an extrapolation of
high field data.Comment: 5 pages, 2 figures, SCES conference proceedin
Temperature and Density Distribution in the Molecular Gas Toward Westerlund 2: Further Evidence for Physical Association
Furukawa et al. 2009 reported the existence of a large mass of molecular gas
associated with the super star cluster Westerlund 2 and the surrounding HII
region RCW49, based on a strong morphological correspondence between NANTEN2
12CO(J=2-1) emission and Spitzer IRAC images of the HII region. We here present
temperature and density distributions in the associated molecular gas at 3.5 pc
resolution, as derived from an LVG analysis of the 12CO(J=2-1), 12CO(J=1-0) and
13CO(J=2-1) transitions. The kinetic temperature is as high as 60-150 K within
a projected distance of 5-10 pc from Westerlund 2 and decreases to as low as 10
K away from the cluster. The high temperature provides robust verification that
the molecular gas is indeed physically associated with the HII region,
supporting Furukawa et al.'s conclusion. The derived temperature is also
roughly consistent with theoretical calculations of photo dissociation regions
(PDRs), while the low spatial resolution of the present study does not warrant
a more detailed comparison with PDR models. We suggest that the molecular
clouds presented here will serve as an ideal laboratory to test theories on
PDRs in future higher resolution studies.Comment: 23 pages, 5 figures, accepted for publication in Ap
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