1,120 research outputs found
Electromagnetic Form Factors of Charged and Neutral Kaons
The charged and neutral kaon form factors are calculated as a
phenomenological application of the QCD Dyson-Schwinger equations. The results
are compared with the pion form factor calculated in the same framework and
yield \mbox{} on
\mbox{~GeV}; and a neutral kaon form factor that is similar in
form and magnitude to the neutron charge form factor. These results are
sensitive to the difference between the kaon and pion Bethe-Salpeter amplitude
and the - and -quark propagation characteristics.Comment: 11 Pages, 2 figures, REVTEX, uses epsfig. No chang
K_{l 3} and \pi_{e 3} transition form factors
and transition form factors are calculated as an
application of Dyson-Schwinger equations. The role of nonanalytic contributions
to the quark--W-boson vertex is elucidated. A one-parameter model for this
vertex provides a uniformly good description of these transitions, including
the value of the scalar form factor of the kaon at the Callan-Treiman point.
The form factors, , are approximately linear on and have approximately the same slope. is a measure
of the Euclidean constituent-quark mass ratio: . In the isospin
symmetric limit: , the electromagnetic pion form factor,
and .Comment: 11 pages (incl. 3 figures), elsart.sty, epsf.st
K -> pi pi and a light scalar meson
We explore the Delta-I= 1/2 rule and epsilon'/epsilon in K -> pi pi
transitions using a Dyson-Schwinger equation model. Exploiting the feature that
QCD penguin operators direct K^0_S transitions through 0^{++} intermediate
states, we find an explanation of the enhancement of I=0 K -> pi pi transitions
in the contribution of a light sigma-meson. This mechanism also affects
epsilon'/epsilon.Comment: 7 pages, REVTE
Nucleon form factors and a nonpointlike diquark
Nucleon form factors are calculated on q^2 in [0,3] GeV^2 using an Ansatz for
the nucleon's Fadde'ev amplitude motivated by quark-diquark solutions of the
relativistic Fadde'ev equation. Only the scalar diquark is retained, and it and
the quark are confined. A good description of the data requires a nonpointlike
diquark correlation with an electromagnetic radius of 0.8 r_pi. The composite,
nonpointlike nature of the diquark is crucial. It provides for diquark-breakup
terms that are of greater importance than the diquark photon absorption
contribution.Comment: 5 pages, REVTEX, epsfig, 3 figure
Goldstone Theorem and Diquark Confinement Beyond Rainbow-Ladder Approximation
The quark Dyson-Schwinger equation and meson Bethe-Salpeter equation are
studied in a truncation scheme that extends the rainbow-ladder approximation
such that, in the chiral limit, the isovector, pseudoscalar meson remains
massless. Quark-quark (diquark) correlations, which are bound in rainbow-ladder
approximation, are destabilised by repulsive contributions that only appear at
higher order in the Bethe-Salpeter kernel. The net effect of higher order terms
on the meson bound-state masses is small.Comment: 11 pages, LaTeX, elsart.sty, 3 EPS figure
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A continuum order parameter for deconfinement
Dyson-Schwinger equations are presented as a non-perturbative tool for the study and modeling of QCD at finite-{ital T}. An order parameter for deconfinement, applicable for both light and heavy quarks, is introduced. In a simple Dyson-Schwinger equation model of two-flavor QCD, coincident, 2nd-order chiral symmetry restoration and deconfinement transitions occur at {ital T} {approx} 150 MeV, with the same critical exponent, {Beta} {approx} 0.33
Valence-quark distributions in the pion
We calculate the pion's valence-quark momentum-fraction probability
distribution using a Dyson-Schwinger equation model. Valence-quarks with an
active mass of 0.30 GeV carry 71% of the pion's momentum at a resolving scale
q_0=0.54 GeV = 1/(0.37 fm). The shape of the calculated distribution is
characteristic of a strongly bound system and, evolved from q_0 to q=2 GeV, it
yields first, second and third moments in agreement with lattice and
phenomenological estimates, and valence-quarks carrying 49% of the pion's
momentum. However, pointwise there is a discrepancy between our calculated
distribution and that hitherto inferred from parametrisations of extant
pion-nucleon Drell-Yan data.Comment: 8 pages, 3 figures, REVTEX, aps.sty, epsfig.sty, minor corrections,
version to appear in PR
Dyson-Schwinger Equations: An Instrument for Hadron Physics
Dyson-Schwinger equations furnish a Poincare' covariant approach to hadron
physics. They reveal that dynamical chiral symmetry breaking is tied to the
long-range behaviour of the strong interaction and make predictions
corroborated by modern lattice-QCD simulations. A hallmark in the contemporary
use of DSEs is the existence of a nonperturbative, symmetry preserving
truncation that enables the proof of exact results. The systematic error
associated with the truncation's leading term has been quantified and this
underpins an efficacious one-parameter model that is being employed to study
meson excited states.Comment: 9 pages; LaTeX2e; Contribution to proceedings of "17th International
Conference on Few-Body Problems in Physics," Duke University/TUNL,
5-10/June/200
Goldstone Boson's Valence-Quark Distribution
Dynamical chiral symmetry breaking (DCSB) is one of the keystones of
low-energy hadronic phenomena. Dyson-Schwinger equations provide a
model-independent quark-level understanding and correlate that with the
behaviour of the pion's Bethe-Salpeter amplitude. This amplitude is a core
element in the calculation of pion observables and combined with the
dressed-quark Schwinger function required by DCSB it yields a valence-quark
distribution function for the pion that behaves as (1-x)^2 for x~1, in
accordance with perturbative analyses. This behaviour can be verified at
contemporary experimental facilities.Comment: 7 pages, LaTeX2e, espcrc2.sty; Summary of a presentation at the 11th
International Light-Cone Workshop: ``Light-cone Physics: Particles and
Strings,'' ECT*, Trento, Italy, 3-11/Nov./200
Looking into the matter of light-quark hadrons
In tackling QCD, a constructive feedback between theory and extant and
forthcoming experiments is necessary in order to place constraints on the
infrared behaviour of QCD's \beta-function, a key nonperturbative quantity in
hadron physics. The Dyson-Schwinger equations provide a tool with which to work
toward this goal. They connect confinement with dynamical chiral symmetry
breaking, both with the observable properties of hadrons, and hence provide a
means of elucidating the material content of real-world QCD. This contribution
illustrates these points via comments on: in-hadron condensates; dressed-quark
anomalous chromo- and electro-magnetic moments; the spectra of mesons and
baryons, and the critical role played by hadron-hadron interactions in
producing these spectra.Comment: 11 pages, 7 figures. Contribution to the Proceedings of "Applications
of light-cone coordinates to highly relativistic systems - LIGHTCONE 2011,"
23-27 May, 2011, Dallas. The Proceedings will be published in Few Body
System
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