1,011 research outputs found
A Determination of the Lambda Parameter from Full Lattice QCD
We present a determination of the QCD parameter Lambda in the quenched
approximation (n_f=0) and for two flavours (n_f=2) of light dynamical quarks.
The calculations are performed on the lattice using O(a) improved Wilson
fermions and include taking the continuum limit. We find Lambda_{n_f=0} =
259(1)(20) MeV and Lambda_{n_f=2} = 261(17)(26) MeV}, using r_0 = 0.467 fm to
set the scale. Extrapolating our results to five flavours, we obtain for the
running coupling constant at the mass of the Z boson alpha_s(m_Z) =
0.112(1)(2). All numbers refer to the MSbar scheme.Comment: 25 pages, 9 figure
Spectra of heavy-light and heavy-heavy mesons containing charm quarks, including higher spin states for
We study the spectra of heavy-light and heavy-heavy mesons containing charm
quarks, including higher spin states. We use two sets of gauge
configurations, one set from QCDSF using the SLiNC action, and the other
configurations from the Budapest-Marseille-Wuppertal collaboration, using the
HEX smeared clover action. To extract information about the excited states, we
choose a suitable basis of operators to implement the variational method.Comment: 7 pages, 5 figures, Talk presented at the XXIX International
Symposium on Lattice Field Theory, Lattice2011, July 11-16, 2011, The Village
at Squaw Valley, California, US
Patterns of regional lung physiology in cystic fibrosis using ventilation magnetic resonance imaging and multiple-breath washout
Hyperpolarised helium-3 (3He) ventilation magnetic resonance imaging (MRI) and multiple-breath washout (MBW) are sensitive methods for detecting lung disease in cystic fibrosis (CF). We aimed to explore their relationship across a broad range of CF disease severity and patient age, as well as assess the effect of inhaled lung volume on ventilation distribution.32 children and adults with CF underwent MBW and 3He-MRI at a lung volume of end-inspiratory tidal volume (EIVT). In addition, 28 patients performed 3He-MRI at total lung capacity. 3He-MRI scans were quantitatively analysed for ventilation defect percentage (VDP), ventilation heterogeneity index (VHI) and the number and size of individual contiguous ventilation defects. From MBW, the lung clearance index, convection-dependent ventilation heterogeneity (Scond) and convection-diffusion-dependent ventilation heterogeneity (Sacin) were calculated.VDP and VHI at EIVT strongly correlated with lung clearance index (r=0.89 and r=0.88, respectively), Sacin (r=0.84 and r=0.82, respectively) and forced expiratory volume in 1 s (FEV1) (r=-0.79 and r=-0.78, respectively). Two distinct 3He-MRI patterns were highlighted: patients with abnormal FEV1 had significantly (p<0.001) larger, but fewer, contiguous defects than those with normal FEV1, who tended to have numerous small volume defects. These two MRI patterns were delineated by a VDP of ∼10%. At total lung capacity, when compared to EIVT, VDP and VHI reduced in all subjects (p<0.001), demonstrating improved ventilation distribution and regions of volume-reversible and nonreversible ventilation abnormalities
Revisiting the Bragg reflector to illustrate modern developments in optics
Copyright © 2014 American Association of Physics TeachersA series of thin layers of alternating refractive index are known to make a good optical mirror over certain bands of frequency. Such a device, often termed the Bragg reflector, is usually introduced to students in isolation from other parts of the curriculum. Here, we show that the basic physics of wave propagation through a stratified medium can be used to illustrate some more modern developments in optics and quantum physics, from transfer matrix techniques to the optical properties of cold trapped atoms and optomechanical cooling. We also show a simple example of how such systems exhibit an appreciable level of optical nonreciprocity.Engineering and Physical Sciences Research Council (EPSRC)National Natural Science Foundation of ChinaNational Basic Research Program of ChinaCRUI-British CouncilAzione Integrata MIURFondo di Ateneo of Brescia Universit
Do we understand the unquenched value of fB?
I review our qualitative understanding of the increase in the value of the B
meson decay constant (fB), when dynamical fermions are included in lattice QCD
calculations.Comment: 4 pages. Talk at UK Phenomenology Workshop on Heavy Flavour and CP
Violation, Durham, 17 - 22 September 2000 (Minor typo fixed
Spectroscopy and Renormalisation Group Flow of a Lattice Nambu-Jona-Lasinio Model
We investigate a lattice Nambu--Jona-Lasinio model both by the Monte Carlo
method and Schwinger-Dyson equations. A comparison allows the discussion of
finite size effects and the extrapolation to infinite volume. We pay special
attention to the identification of particles and resonances. This enables us to
discuss renormalisation group flows in the neighbourhood of the critical
coupling where the chiral symmetry breaking phase transition takes place. In no
region of the bare parameter space do we find renormalisability for the model.Comment: 66 pages, latex and postscript figures. The postscript file for this
paper (called njl.ps) is also available from ftp://dirac.physik.fu-berlin.de/
in the directory nj
Disconnected contributions to D-meson semi-leptonic decay form factors
We calculate the disconnected contribution to the form factor for the
semileptonic decay of a D-meson into a final state, containing a flavor singlet
eta meson. We use QCDSF n_f=2+1 configurations at the flavor symmetric point
m_u=m_d=m_s and the partially quenched approximation for the relativistic charm
quark. Several acceleration and noise reduction techniques for the stochastic
estimation of the disconnected loop are tested.Comment: 7 pages, talk presented at the XXIX International Symposium on
Lattice Field Theory (Lattice 2011), July 10-16, 2011, Squaw Valley, Lake
Tahoe, California, US
Speeding up finite step-size updating of full QCD on the lattice
We propose various improvements of finite step-size updating for full QCD on
the lattice that might turn finite step-size updating into a viable alternative
to the hybrid Monte Carlo algorithm. These improvements are noise reduction of
the noisy estimator of the fermion determinant, unbiased inclusion of the
hopping parameter expansion and a multi-level Metropolis scheme. First
numerical tests are performed for the 2 dimensional Schwinger model with two
flavours of Wilson fermions and for QCD two flavours of Wilson fermions and
Schr"odinger functional boundary conditions.Comment: 22 pages, 1 figur
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