173 research outputs found
Nucleon Tensor Charge from Exclusive Electroproduction
Exclusive electroproduction from nucleons is suggested for extracting
the tensor charge and other quantities related to transversity from
experimental data. This process isolates C-parity odd and chiral odd
combinations of t-channel exchange quantum numbers. In a hadronic picture it
connects the meson production amplitudes to C-odd Regge exchanges with final
state interactions. In a description based on partonic degrees of freedom, the
helicity structure for this C-odd process relates to the quark helicity flip,
or chiral odd generalized parton distributions. This differs markedly from
deeply virtual Compton scattering, and both vector meson and charged
electroproduction, where the axial charge can enter the amplitudes. Contrarily
the tensor charge enters the process. The connection through the
helicity description of the process to both the partonic and hadronic
perspectives is studied and exploited in model calculations to indicate how the
tensor charge and other transversity parameters can be related to cross section
and spin asymmetry measurements over a broad range of kinematics.Comment: 40 pages, 14 figures Revised text clarifying main points, fixing
typos, adding reference
Gluon contributions to the pion mass and light cone momentum fraction
We calculate the matrix elements of the gluonic contributions to the
energy-momentum tensor for a pion of mass 600 < Mpi < 1100 MeV in quenched
lattice QCD. We find that gluons contribute (37 +/- 8 +/- 12)% of the pion's
light cone momentum. The bare matrix elements corresponding to the trace
anomaly contribution to the pion mass are also obtained. The discretizations of
the energy-momentum tensor we use have other promising applications, ranging
from calculating the origin of hadron spin to QCD thermodynamics.Comment: 4 pages, 2 figure
Semileptonic to Nucleon Transitions in Full QCD at Light Cone
The tree level semileptonic and
transitions are investigated using the light cone QCD sum rules approach in
full theory. The spin--1/2, baryon with or , is
considered by the most general form of its interpolating current. The time
ordering product of the initial and transition currents is expanded in terms of
the nucleon distribution amplitudes with different twists. Considering two sets
of independent input parameters entering to the nucleon wave functions, namely,
QCD sum rules and Lattice QCD parameters, the related form factors and their
heavy quark effective theory limits are calculated and compared with the
existing predictions of other approaches. It is shown that our results satisfy
the heavy quark symmetry relations for lattice input parameters and b case
exactly and the maximum violation is for charm case and QCD sum rules input
parameters. The obtained form factors are used to compute the transition rates
both in full theory and heavy quark effective theory. A comparison of the
results on decay rate of with those predicted by other
phenomenological methods or the same method in heavy quark effective theory
with different interpolating current and distribution amplitudes of the
is also presented.Comment: 18 Pages and 16 Table
Hadronic Coupling Constants in Lattice QCD
We calculate the hadronic coupling constants and
in QCD, including dynamical quarks in the framework of staggered fermions in
the lattice approach. For the nucleon--pion coupling we obtain , to be compared with the experimental value . The
coupling has been analysed for two different sets of operators
with the averaged result which is to be compared
with the experimental value .Comment: 14 pages uuencoded postscript fil
Flavor Changing Neutral Currents Transition of the to Nucleon in Full QCD and Heavy Quark Effective Theory
The loop level flavor changing neutral currents transitions of the
and are investigated in full
QCD and heavy quark effective theory in the light cone QCD sum rules approach.
Using the most general form of the interpolating current for ,
or , as members of the recently discovered sextet heavy baryons with
spin 1/2 and containing one heavy quark, the transition form factors are
calculated using two sets of input parameters entering the nucleon distribution
amplitudes, namely, QCD sum rules and lattice QCD inputs. The obtained results
are used to estimate the decay rates of the corresponding transitions. Since
such type transitions occurred at loop level in the standard model, they can be
considered as good candidates to search for the new physics effects beyond the
SM.Comment: 18 Pages and 13 Table
Bayesian approach to the first excited nucleon state in lattice QCD
We present preliminary results from the first attempt to reconstruct the
spectral function in the nucleon and channels from lattice QCD data
using the maximum entropy method (MEM). An advantage of the MEM analysis is to
enable us to access information of the excited state spectrum. Performing
simulations on two lattice volumes, we confirm the large finite size effect on
the first excited nucleon state in the lighter quark mass region.Comment: Lattice2002(spectrum), Latex with espcrc2.sty, 3 pages, 3 figure
Perturbatively improving renormalization constants
Renormalization factors relate the observables obtained on the lattice to
their measured counterparts in the continuum in a suitable renormalization
scheme. They have to be computed very precisely which requires a careful
treatment of lattice artifacts. In this work we present a method to suppress
these artifacts by subtracting one-loop contributions proportional to the
square of the lattice spacing calculated in lattice perturbation theory.Comment: 7 pages, 2 figures, LATTICE 201
Lattice calculation of the lowest order hadronic contribution to the muon anomalous magnetic moment
We present a quenched lattice calculation of the lowest order (alpha^2)
hadronic contribution to the anomalous magnetic moment of the muon which arises
from the hadronic vacuum polarization. A general method is presented for
computing entirely in Euclidean space, obviating the need for the usual
dispersive treatment which relies on experimental data for e^+e^- annihilation
to hadrons. While the result is not yet of comparable accuracy to those
state-of-the-art calculations, systematic improvement of the quenched lattice
computation to this level of accuracy is straightforward and well within the
reach of present computers. Including the effects of dynamical quarks is
conceptually trivial, the computer resources required are not.Comment: 12 pages, including two figures. Added reference and footnote
Replaced with published version; minor changes asked for by referees and
minor deletions to stay within page limi
Generalized Parton Distributions in Full Lattice QCD
We present recent results on generalized parton distributions from dynamical
lattice QCD calculations. Our set of twelve different combinations of couplings
and quark masses allows for a preliminary study of the pion mass dependence of
the transverse nucleon structure.Comment: 8 pages, 5 figures; Talk presented by Ph.H. at Light-Cone 2004,
Amsterdam, 16 - 20 Augus
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