708 research outputs found
A lattice calculation of the pion form factor with Ginsparg-Wilson-type fermions
Results for Monte Carlo calculations of the electromagnetic vector and scalar
form factors of the pion in a quenched simulation are presented. We work with
two different lattice volumes up to a spatial size of 2.4 fm at a lattice
spacing of 0.148 fm. The pion form factors in the space-like region are
determined for pion masses down to 340 MeV.Comment: REVTeX 4, 8 pages, 9 figures, 4 tables; final versio
Nonperturbative improvement and tree-level correction of the quark propagator
We extend an earlier study of the Landau gauge quark propagator in quenched
QCD where we used two forms of the O(a)-improved propagator with the
Sheikholeslami-Wohlert quark action. In the present study we use the
nonperturbative value for the clover coefficient c_sw and mean-field
improvement coefficients in our improved quark propagators. We compare this to
our earlier results which used the mean-field c_sw and tree-level improvement
coefficients for the propagator. We also compare three different
implementations of tree-level correction: additive, multiplicative, and hybrid.
We show that the hybrid approach is the most robust and reliable and can
successfully deal even with strong ultraviolet behavior and zero-crossing of
the lattice tree-level expression. We find good agreement between our improved
quark propagators when using the appropriate nonperturbative improvement
coefficients and hybrid tree-level correction. We also present a simple
extrapolation of the quark mass function to the chiral limit.Comment: 12 pages, 18 figures, RevTeX4. Some clarifications and corrections.
Final version, to appear in Phys.Rev.
Gluon propagator, triple gluon vertex and the QCD coupling constant
We study the UV-scaling of the flavorless gluon propagator in the Landau
gauge in an energy window up to 9 GeV. Dominant hypercubic lattice artifacts
are eliminated. A large set of renormalization schemes is used to test
asymptotic scaling. We compare with our results obtained directly from the
triple gluon vertex. We end-up with \Lambda_{\bar{\rm{MS}}} = 318(12)(5) MeV
and 292(5)(15) MeV respectively for these two methods, compatible which each
other but significantly above the Schrodinger method estimate.Comment: 3 pages, LaTeX with two figures; presented at LATTICE9
Power Corrections to Perturbative QCD and OPE in Gluon Green Functions
We show that QCD Green functions in Landau Gauge exhibit sizable
corrections to the expected perturbative behavior at energies as high as 10
GeV. We argue that these are due to a -condensate which does not vanish
in Landau gauge.Comment: 3 pages 1 figure lattice2001 (gaugetheories
Electrodynamics of superconducting pnictide superlattices
It has been recently reported (S. Lee et al., Nature Materials 12, 392, 2013)
that superlattices where layers of the 8% Co-doped BaFe2As2 superconducting
pnictide are intercalated with non superconducting ultrathin layers of either
SrTiO3 or of oxygen-rich BaFe2As2, can be used to control flux pinning, thereby
increasing critical fields and currents, without significantly affecting the
critical temperature of the pristine superconducting material. However, little
is known about the electron properties of these systems. Here we investigate
the electrodynamics of these superconducting pnictide superlattices in the
normal and superconducting state by using infrared reflectivity, from THz to
visible range. We find that multi-gap structure of these superlattices is
preserved, whereas some significant changes are observed in their electronic
structure with respect to those of the original pnictide. Our results suggest
that possible attempts to further increase the flux pinning may lead to a
breakdown of the pnictide superconducting properties.Comment: 4 pages, two figure
Light Quark Masses from Lattice Quark Propagators at Large Momenta
We compute non-perturbatively the average up-down and strange quark masses
from the large momentum (short-distance) behaviour of the quark propagator in
the Landau gauge. This method, which has never been applied so far, does not
require the explicit calculation of the quark mass renormalization constant.
Calculations were performed in the quenched approximation, by using
O(a)-improved Wilson fermions. The main results of this study are
ml^RI(2GeV)=5.8(6)MeV and ms^RI(2GeV)=136(11)MeV. Using the relations between
different schemes, obtained from the available four-loop anomalous dimensions,
we also find ml^RGI=7.6(8)MeV and ms^RGI=177(14)MeV, and the MSbar-masses,
ml^MS(2GeV)=4.8(5)MeV and ms^MS(2GeV)=111(9)MeV.Comment: 19 pages, 2 references added, version to appear in Phys. Rev.
Asymptotic scaling of the gluon propagtor on the lattice
We pursue the study of the high energy behaviour of the gluon propagator on
the lattice in the Landau gauge in the flavorless case (n_f=0). It was shown in
a precedin g paper that the gluon propagator did not reach three-loop
asymptotic scaling at an energy scale as high as 5 GeV.
Our present high statistics analysis includes also a simulation at
( fm), which allows to reach GeV.
Special care has been devoted to the finite lattice-spacing artifacts as well
as to the finite volume effects, the latter being acute at where
the volume is bounded by technical limits. Our main conclusion is a strong
evidence that the gluon propagator has reached three-loop asymptotic scaling,
at ranging from 5.6 GeV to 9.5 GeV. We buttress up this conclusion on
several demanding criteria of asymptoticity, including scheme independence. Our
fit in the 5.6 GeV to 9.5 GeV window yields MeV, in good agreement with our previous result,
MeV, obtained from the three gluon
vertex, but it is significantly above the Schr\"odinger functional method
estimate : MeV. The latter difference is not understood.
Confirming our previous paper, we show that a fourth loop is necessary to fit
the whole () GeV energy window.Comment: latex-file, 19 pgs., 6 fig
A CVID-associated variant in the ciliogenesis protein CCDC28B disrupts immune synapse assembly
A lattice calculation of vector meson couplings to the vector and tensor currents using chirally improved fermions
We present a quenched lattice calculation of , the coupling of
vector mesons to the tensor current normalized by the vector meson decay
constant. The chirally improved lattice Dirac operator, which allows us to
reach small quark masses, is used. We put emphasis on analyzing the quark mass
dependence of and find only a rather weak dependence. Our
results at the and masses agree well with QCD sum rule
calculations and those from previous lattice studies.Comment: 6 pages, 3 figures, one sentence remove
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