4,659 research outputs found
Scalar Meson Spectroscopy with Lattice Staggered Fermions
With sufficiently light up and down quarks the isovector () and
isosinglet () scalar meson propagators are dominated at large distance by
two-meson states. In the staggered fermion formulation of lattice quantum
chromodynamics, taste-symmetry breaking causes a proliferation of two-meson
states that further complicates the analysis of these channels. Many of them
are unphysical artifacts of the lattice approximation. They are expected to
disappear in the continuum limit. The staggered-fermion fourth-root procedure
has its purported counterpart in rooted staggered chiral perturbation theory
(rSXPT). Fortunately, the rooted theory provides a strict framework that
permits the analysis of scalar meson correlators in terms of only a small
number of low energy couplings. Thus the analysis of the point-to-point scalar
meson correlators in this context gives a useful consistency check of the
fourth-root procedure and its proposed chiral realization. Through numerical
simulation we have measured correlators for both the and channels
in the ``Asqtad'' improved staggered fermion formulation in a lattice ensemble
with lattice spacing fm. We analyze those correlators in the context
of rSXPT and obtain values of the low energy chiral couplings that are
reasonably consistent with previous determinations.Comment: 23 pp., 3 figs., submitted to Phys. Rev.
Anomalous scaling of passive scalar in turbulence and in equilibrium
We analyze multi-point correlation functions of a tracer in an incompressible
flow at scales far exceeding the scale at which fluctuations are generated
(quasi-equilibrium domain) and compare them with the correlation functions at
scales smaller than (turbulence domain). We demonstrate that the scale
invariance can be broken in the equilibrium domain and trace this breakdown to
the statistical integrals of motion (zero modes) as has been done before for
turbulence. Employing Kraichnan model of short-correlated velocity we identify
the new type of zero modes, which break scale invariance and determine an
anomalously slow decay of correlations at large scales
Light hadron properties with improved staggered quarks
Preliminary results from simulations with 2+1 dynamical quark flavors at a
lattice spacing of 0.09 fm are combined with earlier results at a=0.13 fm. We
examine the approach to the continuum limit and investigate the dependence of
the pseudoscalar masses and decay constants as the sea and valence quark masses
are separately varied.Comment: Lattice2002(spectrum
Approximate Killing Vectors on S^2
We present a new method for computing the best approximation to a Killing
vector on closed 2-surfaces that are topologically S^2. When solutions of
Killing's equation do not exist, this method is shown to yield results superior
to those produced by existing methods. In addition, this method appears to
provide a new tool for studying the horizon geometry of distorted black holes.Comment: 4 pages, 3 figures, submitted to Physical Review D, revtex
Heavy-light decay constants using clover valence quarks and three flavors of dynamical improved staggered quarks
Starting in 2001, the MILC Collaboration began a large scale calculation of
heavy-light meson decay constants using clover valence quarks on ensembles of
three flavor configurations. For the coarse configurations, with a=0.12 fm,
eight combinations of dynamical light and strange quarks have been analyzed.
For the fine configurations, with a=0.09 fm, three combinations of quark masses
are studied. Since we last reported on this calculation, statistics have been
increased on the fine ensembles, and, more importantly, a preliminary value for
the perturbative renormalization of the axial-vector current has become
available. Thus, results for f_B, f_{B_s}, f_D and f_{D_s} can, in principle,
be calculated in MeV, in addition to decay-constant ratios that were calculated
previously.Comment: Talk presented at Lattice2004(heavy), Fermilab, June 21-26, 2004; 3
pages, 3 color figure
The beginnings of geography teaching and research in the University of Glasgow: the impact of J.W. Gregory
J.W. Gregory arrived in Glasgow from Melbourne in 1904 to take up the post of foundation Professor of Geology in the University of Glasgow. Soon after his arrival in Glasgow he began to push for the setting up of teaching in Geography in Glasgow, which came to pass in 1909 with the appointment of a Lecturer in Geography. This lecturer was based in the Department of Geology in the University's East Quad. Gregory's active promotion of Geography in the University was matched by his extensive writing in the area, in textbooks, journal articles and popular books. His prodigious output across a wide range of subject areas is variably accepted today, with much of his geomorphological work being judged as misguided to varying degrees. His 'social science' publications - in the areas of race, migration, colonisation and economic development of Africa and Australia - espouse a viewpoint that is unacceptable in the twenty-first century. Nonetheless, that viewpoint sits squarely within the social and economic traditions of Gregory's era, and he was clearly a key 'Establishment' figure in natural and social sciences research in the first half of the twentieth century. The establishment of Geography in the University of Glasgow remains enduring testimony of J.W. Gregory's energy, dedication and foresight
High temperature QCD with three flavors of improved staggered quarks
We present an update of our study of high temperature QCD with three flavors
of quarks, using a Symanzik improved gauge action and the Asqtad staggered
quark action. Simulations are being carried out on lattices with Nt=4, 6 and 8
for the case of three degenerate quarks with masses less than or equal to the
strange quark mass, , and on lattices with Nt=6 and 8 for degenerate up
and down quarks with masses in the range 0.2 m_s \leq m_{u,d} \leq 0.6 m_s, and
the strange quark fixed near its physical value. We also report on first
computations of quark number susceptibilities with the Asqtad action. These
susceptibilities are of interest because they can be related to event-by-event
fluctuations in heavy ion collision experiments. Use of the improved quark
action leads to a substantial reduction in lattice artifacts. This can be seen
already for free fermions and carries over into our results for QCD.Comment: Lattice2002(Non-zero temperature and density
Kissing Balloon Inflation in Percutaneous Coronary Interventions
Bifurcation lesions are the most frequently approached complex coronary lesions in everyday interventional practice. Bifurcations complexity relies essentially on their very specific anatomy that is imperfectly handled by current coronary devices and, despite dedicated techniques and drug-eluting stents, percutaneous coronary interventions directed toward the treatment of bifurcations are technically demanding and require proper execution. Kissing balloon (KB) inflation was the first specific bifurcation technique to have been developed for percutaneous bifurcation interventions and continues to currently play an important role. Indeed, KB has been proposed to optimize stent apposition, improve side branch access while correcting stent deformation or distortion. Over the years, the KB technique has been deeply investigated by many different methods, from bench testing and computer simulations to in vivo intravascular imaging and clinical studies, producing a large amount of data pointing out the benefits and limitations of the technique. We sought to provide here a comprehensive overview of all those aspects
Heavy-light meson decay constants with N_f=3
During the past year the MILC Collaboration has continued its study of
heavy-light meson decay constants with three dynamical quarks. Calculations
have been extended to a second lattice spacing of about 0.09 fm. At this
lattice spacing, there are results in the quenched approximation and for three
sets of dynamical quark mass: m_l=m_s; m_l=0.4 m_s and m_l=0.2 m_s, where m_l
is the light mass for the u and d quarks and m_s is the strange quark mass. At
the coarser lattice spacing, for which results were presented at Lattice 2001,
statistics have been increased for two sets of quark masses and three
additional sets of quark masses have been studied, giving a total of eight
combinations used to interpolate between the quenched and chiral limits. When
these calculations are completed, we can study the decay constants taking into
account both chiral and continuum extrapolations.Comment: Lattice2002(heavyquark), 3 pages, 3 color figures, to appear in the
proceedings of Lattice 200
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