59 research outputs found
Three-particle contributions to the renormalisation of B-meson light-cone distribution amplitudes
We study light-cone distribution amplitudes of heavy-light systems, such as a
B-meson. By an explicit computation, we determine how two-parton distribution
amplitudes mix with three-parton ones at one loop: \phi_+ is shown to mix only
into itself, whereas \phi_- mixes with the difference of three-parton
distribution amplitudes \Psi_A-\Psi_V. We determine the corresponding anomalous
dimension and we check the gauge independence of our result by considering a
general covariant gauge. Finally, we comment on some implications of our result
for phenomenological models of these distribution amplitudes.Comment: 21 pages, 5 figures, some comments and 2 references added, except for
typesetting matches version published in JHE
International Lattice Data Grid
We propose the co-ordination of lattice QCD grid developments in different
countries to allow transparent exchange of gauge configurations in future,
should participants wish to do so. We describe briefly UKQCD's XML schema for
labelling and cataloguing the data. A meeting to further develop these ideas
will be held in Edinburgh on 19/20 December 2002, and will be available over
AccessGrid.Comment: Lattice2002(plenary
Reply to "Comment on `Lattice determination of Sigma - Lambda mixing' "
In this Reply, we respond to the above Comment. Our computation [Phys. Rev. D
91 (2015) 074512] only took into account pure QCD effects, arising from quark
mass differences, so it is not surprising that there are discrepancies in
isospin splittings and in the Sigma - Lambda mixing angle. We expect that these
discrepancies will be smaller in a full calculation incorporating QED effects.Comment: 5 page
The nucleon mass in N_f=2 lattice QCD: finite size effects from chiral perturbation theory
In the framework of relativistic SU(2)_f baryon chiral perturbation theory we
calculate the volume dependence of the nucleon mass up to and including O(p^4).
Since the parameters in the resulting finite size formulae are fixed from the
pion mass dependence of the large volume nucleon masses and from phenomenology,
we obtain a parameter-free prediction of the finite size effects. We present
mass data from the recent N_f=2 simulations of the UKQCD and QCDSF
collaborations and compare these data as well as published mass values from the
dynamical simulations of the CP-PACS and JLQCD collaborations with the
theoretical expectations. Remarkable agreement between the lattice data and the
predictions of chiral perturbation theory in a finite volume is found.Comment: 23 pages, 5 figures; references added + minor corrections; one more
reference added, typo in eq.(25) corrected, additional clarifying remark
QCD with light Wilson quarks on fine lattices (II): DD-HMC simulations and data analysis
In this second report on our recent numerical simulations of two-flavour QCD,
we provide further technical details on the simulations and describe the
methods we used to extract the meson masses and decay constants from the
generated ensembles of gauge fields. Among the topics covered are the choice of
the DD-HMC parameters, the issue of stability, autocorrelations and the
statistical error analysis. Extensive data tables are included as well as a
short discussion of the quark-mass dependence in partially quenched QCD,
supplementing the physics analysis that was presented in the first paper in
this series.Comment: TeX source, 35 pages, figures include
A lattice determination of Sigma - Lambda mixing
Isospin breaking effects in baryon octet (and decuplet) masses are due to a
combination of up and down quark mass differences and electromagnetic effects
and lead to small mass splittings. Between the Sigma and Lambda this mass
splitting is much larger, this being mostly due to their different
wavefunctions. However when isospin is broken, there is a mixing between
between these states. We describe the formalism necessary to determine the QCD
mixing matrix and hence find the mixing angle and mass splitting between the
Sigma and Lambda particles due to QCD effects.Comment: 40 pages, 5 figures, published versio
A Feynman-Hellmann approach to the spin structure of hadrons
We perform a Nf = 2 + 1 lattice QCD simulation to determine the quark spin
fractions of hadrons using the Feynman-Hellmann theorem. By introducing an
external spin operator to the fermion action, the matrix elements relevant for
quark spin fractions are extracted from the linear response of the hadron
energies. Simulations indicate that the Feynman-Hellmann method offers
statistical precision that is comparable to the standard three-point function
approach, with the added benefit that it is less susceptible to excited state
contamination. This suggests that the Feynman-Hellmann technique offers a
promising alternative for calculations of quark line disconnected contributions
to hadronic matrix elements. At the SU(3)-flavour symmetry point, we find that
the connected quark spin fractions are universally in the range 55-70% for
vector mesons and octet and decuplet baryons. There is an indication that the
amount of spin suppression is quite sensitive to the strength of SU(3)
breaking.Comment: 13 pages, 7 figure
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