8,884 research outputs found
NRQCD results on the MILC extra coarse ensemble
We present preliminary results using NRQCD to describe heavy quarks on the
MILC 2+1 flavour dynamical extra coarse ensemble. We calculate the spectra of
low lying states in bottomonium to complement earlier results on the finer MILC
ensembles. We then exploit the coarseness of the lattices to calculate charm
propagators using NRQCD. These are used to examine the charmonium spectrum and
to calclate the mass of the using NRQCD. Finally we look breifly at the
and systems using the imporoved staggered formalism to describe the
light valence quarks.Comment: 6 pages, Talk presented at Lattice 2005 (Heavy Quarks), Dublin, 25-30
July 200
Heavy-Light Meson Semileptonic Decays with Staggered Light Quarks
We report on exploratory studies of heavy-light meson semileptonic decays
using Asqtad light quarks, NRQCD heavy quarks and Symanzik improved glue on
coarse quenched lattices. Oscillatory contributions to three-point correlators
coming from the staggered light quarks are found to be handled well by Bayesian
fitting methods. B meson decays to both the Goldstone pion and to one of the
point-split non-Goldstone pions are investigated. One-loop perturbative
matching of NRQCD/Asqtad heavy-light currents is incorporated.Comment: 3 pages, 3 postscript figures, Lattice2003(heavy
Infrared Quasi Fixed Points and Mass Predictions in the MSSM II: Large tan(beta) Scenario
We consider the infrared quasi fixed point solutions of the renormalization
group equations for the Yukawa couplings and soft supersymmetry breaking
parameters in the MSSM in the \underline{large } regime. The
existence of IR quasi fixed points together with the values of gauge couplings,
third generation quarks, lepton and Z-boson masses allows one to predict masses
of the Higgs bosons and SUSY particles as functions of the only free parameter,
, or the gluino mass. The lightest Higgs boson mass for TeV is found to be GeV for and
GeV for .Comment: 15 pages, LateX file with 4 eps figures, corrected numbers, new
column in table, last versio
The B_s and D_s decay constants in 3 flavor lattice QCD
Capitalizing on recent advances in lattice QCD, we present a calculation of
the leptonic decay constants f_{B_s} and f_{D_s} that includes effects of one
strange sea quark and two light sea quarks. The discretization errors of
improved staggered fermion actions are small enough to simulate with 3
dynamical flavors on lattices with spacings around 0.1 fm using present
computer resources. By shedding the quenched approximation and the associated
lattice scale ambiguity, lattice QCD greatly increases its predictive power.
NRQCD is used to simulate heavy quarks with masses between 1.5 m_c and m_b. We
arrive at the following results: f_{B_s} = 260 \pm 7 \pm 26 \pm 8 \pm 5 MeV and
f_{D_s} = 290 \pm 20 \pm 29 \pm 29 \pm 6 MeV. The first quoted error is the
statistical uncertainty, and the rest estimate the sizes of higher order terms
neglected in this calculation. All of these uncertainties are systematically
improvable by including another order in the weak coupling expansion, the
nonrelativistic expansion, or the Symanzik improvement program.Comment: 4 page
Heavy-light Mesons and Baryons with b quarks
We present lattice results for the spectrum of mesons containing one heavy
quark and of baryons containing one or two heavy quarks. The calculation is
done in the quenched approximation using the NRQCD formalism for the heavy
quark. We analyze the dependence of the mass splittings on both the heavy and
the light quark masses. Meson P-state fine structure and baryon hyperfine
splittings are resolved for the first time. We fix the b quark mass using both
M_B and M_{\Lambda_b}, and our best estimate is m_b^\MSbar(m_b^\MSbar) =
4.35(10)({}^{-3}_{+2})(10) GeV. The spectrum, obtained by interpolation to m_b,
is compared with the experimental data.Comment: 34 pages, LaTeX, 13 postscript figures, version as publish in Phys.
Rev.
Hyperstrong Radio-Wave Scattering in the Galactic Center. II. A Likelihood Analysis of Free Electrons in the Galactic Center
The scattering diameters of Sgr A* and several nearby OH masers (~ 1" at 1
GHz) indicate that a region of enhanced scattering is along the line of sight
to the Galactic center. We combine radio-wave scattering data and free-free
emission and absorption measurements in a likelihood analysis that constrains
the following parameters of the GC scattering region: The GC-scattering region
separation, d; the angular extent of the region, \psi_l; the outer scale on
which density fluctuations occur, l_0; and the gas temperature, T. The maximum
likelihood estimates of these parameters are d = 133_{-80}^{+200} pc, 0.5
degrees <= \psi_l <~ 1 degrees, and (l_0/1 pc)^{2/3}T^{-1/2} = 10^{-7 +/- 0.8}.
As host media for the scattering, we consider the photoionized surface layers
of molecular clouds and the interfaces between molecular clouds and the 10^7 K
ambient gas. We are unable to make an unambiguous determination, but we favor
an interface model in which the scattering medium is hot (T ~ 10^6 K) and dense
(n_e ~ 10 cm^{-3}). The GC scattering region produces a 1 GHz scattering
diameter for an extragalactic source of 90", if the region is a single screen,
or 180", if the region wraps around the GC, as appears probable. We modify the
Taylor-Cordes model for the Galactic distribution of free electrons in order to
include an explicit GC component. Pulsars seen through this region will have a
dispersion measure of approximately 2000 pc cm^{-3}, of which 75% arises from
the GC component. We stress the uniqueness of the GC scattering region,
probably resulting from the high-pressure environment in the GC.Comment: 39 pages with 9 PostScript figures; LaTeX2e with AASTeX macro aaspp4,
to be published in Ap
Accurate Determinations of from Realistic Lattice QCD
We obtain a new value for the QCD coupling constant by combining lattice QCD
simulations with experimental data for hadron masses. Our lattice analysis is
the first to: 1) include vacuum polarization effects from all three light-quark
flavors (using MILC configurations); 2) include third-order terms in
perturbation theory; 3) systematically estimate fourth and higher-order terms;
4) use an unambiguous lattice spacing; and 5) use an \order(a^2)-accurate QCD
action. We use 28~different (but related) short-distance quantities to obtain
.Comment: 4 pages, 2 figures, 1 table. The revised version differs from the
original because we now use 4-loop beta functions (rather than 3-loop). This
shifts the answer a little (mostly from the evolution from the lattice scale
to M_z -- lattice results aren't very different) and reduces the error
slightl
Comparison of traditional fecal culture, Danish mix-ELISA and SalAD for determination of Salmonella enterica prevalence in growing swine
The goal of this study was to describe and compare serum antibody response (as determined by the Danish Mix-ELISA and the SalAD) to fecal shedding of S. enterica during the growing period in commercially raised, naturally infected swine. Longitudinal investigations of 5 groups of growing pigs in 2, three-site swine production systems were conducted. At the time of submission, fecal culture and Mix-ELISA (at OD ≥ 10 and ≥ 40) results were complete. Fifteen different serotypes were isolated from the 2 systems; the most frequently isolated serotypes were Mbandaka and Typhimurium var Copenhagen. Pig prevalence estimates by fecal culture and Mix-ELISA ranged from 0-48.1%, and 0-84% respectively. Visual analysis of graphical data demonstrates that prevalence estimates based on the Mix-ELISA and fecal culture were similar in pattern throughout the growing phase
The impact of neighbourhood walkability on the effectiveness of a structured education programme to increase objectively measured walking
Background: Incorporating physical activity into daily activities is key for the effectiveness of lifestyle education interventions aimed at improving health outcomes; however, consideration of the environmental context in which individuals live is not always made. Walkability is a characteristic of the physical environment, and may be a potential facilitator to changing physical activity levels. Methods: Using data collected during the Walking Away from Diabetes randomised controlled trial, we examined the association between the walkability of the home neighbourhood and physical activity of participants. We also determined whether home neighbourhood walkability of participants was associated with the intervention effect of the education programme. Results: Data from 706 participants were available for analysis. Neighbourhood walkability was not significantly associated with any of the physical activity measures at baseline, or at 12, 24 or 36 months following the intervention (p>0.05 for all). There was no association between walkability and change in purposeful steps/ day from baseline to 36months in the usual care or intervention arm; 25.77 (-99.04, 150.58) and 42.97 (-327.63, 413.45) respectively. Conclusion: Neighbourhood walkability appeared to have no association with objectively-measured physical activity in this population. Furthermore, the walkability of participant’s neighbourhood did not influence the effectiveness of a lifestyle programme
G359.87+0.18: An FR II Radio Galaxy 15 Arcminutes from Sgr A*. Implications for the Scattering Region in the Galactic Center
G359.87+0.18 is an enigmatic object located 15' from Sgr A*. It has been
variously classified as an extragalactic source, Galactic jet source, and young
supernova remnant. We present new observations of G359.87+0.18 between 0.33 and
15 GHz and use these to argue that this source is an Faranoff-Riley II radio
galaxy. We are able to place a crude limit on its redshift of z > 0.1. The
source has a spectral index \alpha < -1 (S \propto \nu^\alpha), suggestive of a
radio galaxy with a redshift z >~ 2.
The scattering diameters of Sgr A* and several nearby OH masers (~ 1" at 1
GHz) indicate that a region of enhanced scattering is along the line of sight
to the Galactic center. If the region covers the Galactic center uniformly, the
implied diameter for a background source is at least 600" at 0.33 GHz, in
contrast with the observed 20" diameter of G359.87+0.18. Using the scattering
diameter of a nearby OH maser OH 359.762+0.120 and the widths of two, nearby,
non-thermal threads, G0.08+0.15 and G359.79+0.17, we show that a uniform
scattering region should cover G359.87+0.18. We therefore conclude that the
Galactic center scattering region is inhomogeneous on a scale of 5' (~ 10 pc at
a distance of 8.5 kpc). This scale is comparable to the size scale of molecular
clouds in the Galactic center. The close agreement between these two lengths
scales is an indication that the scattering region is linked intimately to the
Galactic center molecular clouds.Comment: Accepted for publication in the ApJ, vol. 515, LaTeX2e manuscript
using aaspp4 macro, 19 pages, 8 figures in 11 PostScript file
- …