242 research outputs found
Spatial Equilibrium Analysis of the World Durum Industry Under Alternative Export Policies
International Relations/Trade,
Color-suppression of non-planar diagrams in bosonic bound states
We study the suppression of non-planar diagrams in a scalar QCD model of a
meson system in space-time dimensions due to the inclusion of the color
degrees of freedom. As a prototype of the color-singlet meson, we consider a
flavor-nonsinglet system consisting of a scalar-quark and a scalar-antiquark
with equal masses exchanging a scalar-gluon of a different mass, which is
investigated within the framework of the homogeneous Bethe-Salpeter equation.
The equation is solved by using the Nakanishi representation for the manifestly
covariant bound-state amplitude and its light-front projection. The resulting
non-singular integral equation is solved numerically. The damping of the impact
of the cross-ladder kernel on the binding energies are studied in detail. The
color-suppression of the cross-ladder effects on the light-front wave function
and the elastic electromagnetic form factor are also discussed. As our results
show, the suppression appears significantly large for , which supports
the use of rainbow-ladder truncations in practical nonperturbative calculations
within QCD.Comment: 12 pages, 7 figures. To appear in Physics Letters
Pauli-Villars Regularization Elucidated in Bopp-Podolsky's Generalized Electrodynamics
We discuss an inherent Pauli-Villars regularization in Bopp-Podolsky's
generalized electrodynamics. Introducing gauge-fixing terms for Bopp-Podolsky's
generalized electrodynamic action, we realize a unique feature for the
corresponding photon propagator with a built-in Pauli-Villars regularization
independent of the gauge choice made in Maxwell's usual electromagnetism.
According to our realization, the length dimensional parameter associated
with Bopp-Podolsky's higher order derivatives corresponds to the inverse of the
Pauli-Villars regularization mass scale , i.e. .
Solving explicitly the classical static Bopp-Podolsky's equations of motion for
a specific charge distribution, we explore the physical meaning of the
parameter in terms of the size of the charge distribution. As an offspring
of the generalized photon propagator analysis, we also discuss our findings
regarding on the issue of the two-term vs. three-term photon propagator in
light-front dynamics
Equivalence of pion loops in equal-time and light-front dynamics
We demonstrate the equivalence of the light-front and equal-time formulations
of pionic corrections to nucleon properties. As a specific example, we consider
the self-energy of a nucleon dressed by pion loops, for both pseudovector and
pseudoscalar pion-nucleon couplings. We derive the leading and next-to-leading
nonanalytic behavior of the self-energy on the light-front, and show explicitly
their equivalence in the rest frame and infinite momentum frame in equal-time
quantization, as well as in a manifestly covariant formulation.Comment: 25 pages, 2 figures; typos corrected in Eqs. (A5), (A6), (A8
On flavor conservation in weak interaction decays involving mixed neutrinos
In the context of quantum field theory (QFT), we compute the amplitudes of
weak interaction processes such as and by using different representations of
flavor states for mixed neutrinos. Analyzing the short time limit of the above
amplitudes, we find that the neutrino states defined in QFT as eigenstates of
the flavor charges lead to results consistent with lepton charge conservation.
On the contrary, the Pontecorvo flavor states produce a violation of lepton
charge in the vertex, which is in contrast with what expected at tree level in
the Standard Model.Comment: 15 page
Non-leptonic two-body decays of the Bc meson in light-front quark model and QCD factorization approach
We study exclusive non-leptonic two-body
decays with (pseudoscalar or vector meson) being factored out in QCD
factorization approach. The non-leptonic decay amplitudes are related to the
product of meson decay constants and the form factors for semileptonic
decays. As inputs in obtaining the branching ratios for a large set of
non-leptonic decays, we use the weak form factors for the semileptonic
decays in the whole kinematical region and the
unmeasured meson decay constants obtained from our previous light-front quark
model. We compare our results of the branching ratios with those of other
theoretical studies.Comment: 11 pages, 3 figures, minor corrections, version to appear in PR
Quantum Field Theory of Meson Mixing
We have developed a quantum field theoretic framework for scalar and
pseudoscalar meson mixing and oscillations in time. The unitary inequivalence
of the Fock space of base (unmixed) eigenstates and the physical mixed
eigenstates is proven and shown to lead to a rich condensate structure. This is
exploited to develop formulas for two flavor boson oscillations in systems of
arbitrary boson occupation number. The mixing and oscillation can be understood
in terms of vacuum condensate which interacts with the bare particles to induce
non-trivial effects. We apply these formulas to analyze the mixing of
with and comment on the system. In addition, we consider the
mixing of boson coherent states, which may have future applications in the
construction of meson lasers.Comment: 12 pages, 3 figures; Eqs.(10-12) corrected, leading to new physical
insights; added paragraph under Eq.(24) explaining physical interpretation of
mixing in terms of vacuum condensation; references added and minor typo
correcte
Renormalized Effective QCD Hamiltonian: Gluonic Sector
Extending previous QCD Hamiltonian studies, we present a new renormalization
procedure which generates an effective Hamiltonian for the gluon sector. The
formulation is in the Coulomb gauge where the QCD Hamiltonian is renormalizable
and the Gribov problem can be resolved. We utilize elements of the Glazek and
Wilson regularization method but now introduce a continuous cut-off procedure
which eliminates non-local counterterms. The effective Hamiltonian is then
derived to second order in the strong coupling constant. The resulting
renormalized Hamiltonian provides a realistic starting point for approximate
many-body calculations of hadronic properties for systems with explicit gluon
degrees of freedom.Comment: 25 pages, no figures, revte
XANES and EXAFS study of a platinum phthalocyanine
Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) studies on [octa(2-ethylhexyloxy)phthalocyaninato]platinum [PtL] as a film at room temperature suggest that the structure consists of non-planar, concave discotic molecules packed perpendicular to the stacking axis.Peer reviewedChemistr
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