67 research outputs found
Dynamical relativistic corrections to the leptonic decay width of heavy quarkonia
We calculate the dynamical relativistic corrections, originating from
radiative one-gluon-exchange, to the leptonic decay width of heavy quarkonia in
the framework of a covariant formulation of Light-Front Dynamics. Comparison
with the non-relativistic calculations of the leptonic decay width of J=1
charmonium and bottomonium S-ground states shows that relativistic corrections
are large. Most importantly, the calculation of these dynamical relativistic
corrections legitimate a perturbative expansion in , even in the
charmonium sector. This is in contrast with the ongoing belief based on
calculations in the non-relativistic limit. Consequences for the ability of
several phenomenological potential to describe these decays are drawn.Comment: 17 pages, 7 figure
Generalized Parton Distributions of the Pion
Off-forward structure functions of the pion are investigated in twist-two and
twist-three approximation. A simple model is used for the pion, which allows to
introduce finite size effects, while preserving gauge invariance. Results for
the imaginary parts of the gamma^* pi -> gamma^* pi off-forward amplitude and
of the structure functions are presented. Generalized Callan-Gross relations
are obtained.Comment: 4 pages, 5 figures, LaTeX, uses espcrc2.sty (included), presented at
QCD03 Conference, Montpellier, France, July 200
Complete analysis of spin structure function g1 of He-3
We present a comprehensive analysis of the nuclear effects important in DIS
on polarized He-3 over a wide range of Bjorken x, 10^{-4} \leq x \leq 0.8.
Effects relevant for the extraction of the neutron spin structure function,
g1^n, from the He-3 data are emphasized.Comment: 30 pages, 6 figures, LaTe
A Model for the Off-forward Structure Functions of the Pion
We extend our model for the pion, which we used previously to calculate its
diagonal structure function, to the off-forward case. The imaginary part of the
off-forward gamma* pi -> gamma* pi scattering amplitude is evaluated in the
chiral limit (m_pi=0) and related to the twist-two and twist-three generalised
parton distributions, H, H3, H3tilde. Non-perturbative effects, linked to the
size of the pion and still preserving gauge invariance, are included.
Remarkable new relations between H, H3 and H3tilde are obtained and discussed.Comment: 9 pages, 20 figures, LaTeX, uses ulg_ptf.cls (included); v2: Form
factors dropped in favour of GPD's, comparison between Wandzura-Wilczek
approximation and our relations adde
A Model for the Generalized Parton Distribution of the Pion
We calculate the off-forward structure function of the pion within a simple
model where the size of the pion is accounted for using a momentum cut-off.
Twist-two and twist-three generalized parton distributions are extracted.
Relations between twist-three and twist-two contributions are obtained, the
origin of which is not kinematical as they differ from those arising from the
Wandzura-Wilczek approximation.Comment: Presented at 6th Conference on Quark Confinement and the Hadron
Spectrum, Villasimius, Sardinia, Italy, 21-25 Sep 2004, 3 pages, 4 figures,
LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty (included
Comparison of gluon flux-tube distributions for quark-diquark and quark-antiquark hadrons
The distribution of gluon fields in hadrons is of fundamental interest in
QCD. Using lattice QCD we have observed the formation of gluon flux tubes
within 3 quark (baryon) and quark plus antiquark (meson) systems for a wide
variety of spatial distributions of the color sources. In particular we have
investigated three quark configurations where two of the quarks are close
together and the third quark is some distance away, which approximates a quark
plus diquark string. We find that the string tension of the quark-diquark
string is the same as that of the quark-antiquark string on the same lattice.
We also compare the longitudinal and transverse profiles of the gluon flux
tubes for both sets of strings, and find them to be of similar radii and to
have similar vacuum suppression.Comment: 6 pages, 9 figures and 1 tabl
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