7,318 research outputs found
Mass renormalisation for improved staggered quarks
Improved staggered quark actions are designed to suppress flavour changing
strong interactions. We discuss the perturbation theory for this type of
actions and show the improvements to reduce the quark mass renormalisation
compared to naive staggered quarks. The renormalisations are of similar size as
for Wilson quarks.Comment: LaTeX, 3 pages, Lattice2001(spectrum
Highly Improved Staggered Quarks on the Lattice, with Applications to Charm Physics
We use perturbative Symanzik improvement to create a new staggered-quark
action (HISQ) that has greatly reduced one-loop taste-exchange errors, no
tree-level order a^2 errors, and no tree-level order (am)^4 errors to leading
order in the quark's velocity v/c. We demonstrate with simulations that the
resulting action has taste-exchange interactions that are at least 3--4 times
smaller than the widely used ASQTAD action. We show how to estimate errors due
to taste exchange by comparing ASQTAD and HISQ simulations, and demonstrate
with simulations that such errors are no more than 1% when HISQ is used for
light quarks at lattice spacings of 1/10 fm or less. The suppression of (am)^4
errors also makes HISQ the most accurate discretization currently available for
simulating c quarks. We demonstrate this in a new analysis of the psi-eta_c
mass splitting using the HISQ action on lattices where a m_c=0.43 and 0.66,
with full-QCD gluon configurations (from MILC). We obtain a result of~111(5)
MeV which compares well with experiment. We discuss applications of this
formalism to D physics and present our first high-precision results for D_s
mesons.Comment: 21 pages, 8 figures, 5 table
The B Meson Decay Constant from Unquenched Lattice QCD
We present determinations of the B meson decay constant f_B and of the ratio
f_{B_s}/f_B using the MILC collaboration unquenched gauge configurations which
include three flavors of light sea quarks. The mass of one of the sea quarks is
kept around the strange quark mass, and we explore a range in masses for the
two lighter sea quarks down to m_s/8.
The heavy b quark is simulated using Nonrelativistic QCD, and both the
valence and sea light quarks are represented by the highly improved (AsqTad)
staggered quark action.
The good chiral properties of the latter action allow for a much smoother
chiral extrapolation to physical up and down quarks than has been possible in
the past. We find f_B = 216(9)(19)(4) (6) MeV and f_{B_s} /f_B = 1.20(3)(1).Comment: 4 pages, 2 figure
On the strange quark mass with improved staggered quarks
We present results on the sum of the masses of light and strange quark using
improved staggered quarks. Our calculation uses 2+1 flavours of dynamical
quarks. The effects of the dynamical quarks are clearly visible.Comment: Lattice2002(spectrum) Latex 3 pages, 2 figure
Unquenching effects on the coefficients of the L\"uscher-Weisz action
The effects of unquenching on the perturbative improvement coefficients in
the Symanzik action are computed within the framework of L\"uscher-Weisz
on-shell improvement. We find that the effects of quark loops are surprisingly
large, and their omission may well explain the scaling violations observed in
some unquenched studies.Comment: 7 pages, 5 figures, uses revtex4; version to appear in Phys.Rev.
From Spinor Geometry to Complex General Relativity
An attempt is made of giving a self-contained (although incomplete)
introduction to holomorphic ideas in general relativity, following work over
the last thirty years by several authors. The main topics are complex
manifolds, two-component spinor calculus, conformal gravity, alpha-planes in
Minkowski space-time, alpha-surfaces and twistor geometry, anti-self-dual
space-times and Penrose transform, spin-3/2 potentials, heaven spaces and
heavenly equations.Comment: With kind permission from Springer Science and Business Media to use
material in the first 5 sections taken from the 1995 Kluwer book "Complex
General Relativity" by G. Esposito. In the revised version, 11 References
have been adde
Major air pollutants and risk of COPD exacerbations: a systematic review and meta-analysis
published_or_final_versio
First determination of the strange and light quark masses from full lattice QCD
We compute the strange quark mass and the average of the and
quark masses using full lattice QCD with three dynamical quarks
combined with experimental values for the pion and kaon masses. The simulations
have degenerate and quarks with masses as low as
, and two different values of the lattice spacing. The bare lattice
quark masses obtained are converted to the \msbar scheme using perturbation
theory at . Our results are: m_s^\msbar(2 GeV) = 76(0)(3)(7)(0)
MeV, \hat m^\msbar(2 GeV) = 2.8(0)(1)(3)(0) MeV and =
27.4(1)(4)(0)(1), where the errors are from statistics, simulation,
perturbation theory, and electromagnetic effects, respectively.Comment: 5 pages, revtex, 2 figures. v2: New ms/hat(m) discussion and
reference, v3: slight change in discussion of referenc
Field Scanner Design for MUSTANG of the Green Bank Telescope
MUSTANG is a bolometer camera for the Green Bank Telescope (GBT) working at a
frequency of 90 GHz. The detector has a field of view of 40 arcseconds. To
cancel out random emission change from atmosphere and other sources, requires a
fast scanning reflecting system with a few arcminute ranges. In this paper, the
aberrations of an off-axis system are reviewed. The condition for an optimized
system is provided. In an optimized system, as additional image transfer
mirrors are introduced, new aberrations of the off-axis system may be
reintroduced, resulting in a limited field of view. In this paper, different
scanning mirror arrangements for the GBT system are analyzed through the ray
tracing analysis. These include using the subreflector as the scanning mirror,
chopping a flat mirror and transferring image with an ellipse mirror, and
chopping a flat mirror and transferring image with a pair of face-to-face
paraboloid mirrors. The system analysis shows that chopping a flat mirror and
using a well aligned pair of paraboloids can generate the required field of
view for the MUSTUNG detector system, while other systems all suffer from
larger off-axis aberrations added by the system modification. The spot diagrams
of the well aligned pair of paraboloids produced is only about one Airy disk
size within a scanning angle of about 3 arcmin.Comment: 7 pages, 9 figure
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