40 research outputs found
Role of diquark correlations and the pion cloud in nucleon elastic form factors
Electromagnetic form factors of the nucleon in the space-like region are
investigated within the framework of a covariant and confining
Nambu-Jona-Lasinio model. The bound state amplitude of the nucleon is obtained
as the solution of a relativistic Faddeev equation, where diquark correlations
appear naturally as a consequence of the strong coupling in the colour
channel. Pion degrees of freedom are included as a perturbation
to the "quark-core" contribution obtained using the Poincar\'e covariant
Faddeev amplitude. While no model parameters are fit to form factor data,
excellent agreement is obtained with the empirical nucleon form factors
(including the magnetic moments and radii) where pion loop corrections play a
critical role for GeV. Using charge symmetry, the nucleon
form factors can be expressed as proton quark sector form factors. The latter
are studied in detail, leading, for example, to the conclusion that the
-quark sector of the Dirac form factor is much softer than the -quark
sector, a consequence of the dominance of scalar diquark correlations in the
proton wave function. On the other hand, for the proton quark sector Pauli form
factors we find that the effect of the pion cloud and axialvector diquark
correlations overcomes the effect of scalar diquark dominance, leading to a
larger -quark anomalous magnetic moment and a form factor in the -quark
sector that is slightly softer than in the -quark sector.Comment: 30 pages and 40 figure
Transverse Momentum Dependent Fragmentation and Quark Distribution Functions from the NJL-jet Model
Using the model of Nambu and Jona-Lasinio to provide a microscopic
description of both the structure of the nucleon and of the quark to hadron
elementary fragmentation functions, we investigate the transverse momentum
dependence of the unpolarized quark distributions in the nucleon and of the
quark to pion and kaon fragmentation functions. The transverse momentum
dependence of the fragmentation functions is determined within a Monte Carlo
framework, with the notable result that the average of the produced
kaons is significantly larger than that of the pions. We also find that
has a sizable $z$ dependence, in contrast with the naive Gaussian
ansatz for the fragmentation functions. Diquark correlations in the nucleon
give rise to a non-trivial flavor dependence in the unpolarized transverse
momentum dependent quark distribution functions. The of the quarks in
the nucleon are also found to have a sizable dependence. Finally, these
results are used as input to a Monte Carlo event generator for semi-inclusive
deep inelastic scattering (SIDIS), which is used to determine the average
transverse momentum squared of the produced hadrons measured in SIDIS, namely
. Again we find that the average of the produced kaons in
SIDIS is significantly larger than that of the pions and in each case \la
P_T^2 \ra has a sizable dependence.Comment: 13 pages, 17 figures, v2: minor revisions to conform with the
published version in Phys.Rev.
Effects of charge symmetry breaking on form factors of the pion and kaon
Effects of charge symmetry breaking associated with the and quark
mass difference in the elastic form factors of the pion and kaon are presented.
We use a confining version of the Nambu--Jona-Lasinio model. The pion and kaon
are described as a dressed quark and antiquark bound states governed by the
Bethe-Salpeter equation, and exhibit the properties of Goldstone bosons, with
the pion mass difference given by as demanded by dynamical chiral symmetry breaking. We found
significant charge symmetry breaking effects for realistic current quark mass
ratios () in the quark electromagnetic form factors of the
pion and kaon. We also report the effects of charge symmetry breaking on the
parton distribution functions, which are rather smaller than those found in the
electromagnetic form factors.Comment: 4 pages, 5 figures, accepted version for the QNP2018 proceedings, 8th
International Conference on Quarks and Nuclear Physics (QNP2018), November
13-17, 2018, Tsukuba, Ibaraki, Japa