1,694 research outputs found
Vector mesons in a relativistic point-form approach
We apply the point form of relativistic quantum mechanics to develop a
Poincare invariant coupled-channel formalism for two-particle systems
interacting via one-particle exchange. This approach takes the exchange
particle explicitly into account and leads to a generalized eigenvalue equation
for the Bakamjian-Thomas type mass operator of the system. The coupling of the
exchange particle is derived from quantum field theory. As an illustrative
example we consider vector mesons within the chiral constituent quark model in
which the hyperfine interaction between the confined quark-antiquark pair is
generated by Goldstone-boson exchange. We study the effect of retardation in
the Goldstone-boson exchange by comparing with the commonly used instantaneous
approximation. As a nice physical feature we find that the problem of a too
large - splitting can nearly be avoided by taking the dynamics of
the exchange meson explicitly into account.Comment: 14 pages, 1 figur
Point-form quantum field theory
We examine canonical quantization of relativistic field theories on the
forward hyperboloid, a Lorentz-invariant surface of the form . This choice of quantization surface implies that all components of the
4-momentum operator are affected by interactions (if present), whereas rotation
and boost generators remain interaction free -- a feature characteristic of
Dirac's `` point-form\rq\rq of relativistic dynamics. Unlike previous attempts
to quantize fields on space-time hyperboloids, we keep the usual plane-wave
expansion of the field operators and consider evolution of the system generated
by the 4-momentum operator. We verify that the Fock-space representations of
the Poincar\'e generators for free scalar and spin-1/2 fields look the same as
for equal-time quantization. Scattering is formulated for interacting fields in
a covariant interaction picture and it is shown that the familiar perturbative
expansion of the S-operator is recovered by our approach. An appendix analyzes
special distributions, integrals over the forward hyperboloid, that are used
repeatedly in the paper.Comment: 30 page
Bridges and Barriers: Patients\u27 Perceptions of the Discharge Process Including Multidisciplinary Rounds on a Trauma Unit
Discharge planning is a complex process and ideally begins early in the patient stay. Despite evidence about the importance of discharge readiness, there is limited literature about the patient\u27s view during this transition. The goal of this study was to explore patient perspectives about the discharge process, including multidisciplinary rounds. Multidisciplinary rounding is a process where care providers from various specialties meet to communicate, coordinate patient care, make decisions, and manage responsibilities. The theme found was âbridges and barriers to discharge.â Participants identified timelines and tasks, communication, social support, and motivation as helpful and medical setbacks, insurance limitations, and infrequent communication as hindrances to the discharge. Future research is recommended examining efficacy of various discharge models and examination of communication and support throughout hospitalization
Electroweak properties of baryons in a covariant chiral quark model
The proton and neutron electromagnetic form factors and the nucleon axial
form factor have been calculated in the Goldstone-boson exchange
constituent-quark model within the point-form approach to relativistic quantum
mechanics. The results, obtained without any adjustable parameter nor quark
form factors, are, due to the dramatic effects of the boost required by the
covariant treatment, in striking agreement with the data.Comment: Proceedings of the Conference N*2001, Mainz; 4 pages, 3 figures
included in eps format; World Scientific style file include
Nucleon electromagnetic and axial form factors in point-form relativistic quantum mechanics
Results for the proton and neutron electric and magnetic form factors as well
as the nucleon axial form factor are presented for constituent quark models,
based on either one-gluon-exchange and Goldstone-boson-exchange dynamics. The
calculations are performed in a covariant framework using the point-form
approach to relativistic quantum mechanics. The only input to the calculations
is the nucleon wave function of the corresponding constituent quark model. A
comparison is given to results of the instanton-induced constituent quark model
treated with the Bethe-Salpeter equation.Comment: 4 pages, 6 figures, contribution to XVIII European Conference on
Few-Body Problems in Physics, September 2002, Bled, Sloveni
Covariant nucleon electromagnetic form factors from the Goldstone-boson-exchange quark model
We present a study of proton and neutron electromagnetic form factors for the
recently proposed Goldstone-boson-exchange constituent quark model. Results for
charge radii, magnetic moments, and electric as well as magnetic form factors
are reported. The calculations are performed in a covariant framework using the
point-form approach to relativistic quantum mechanics. All the predictions by
the Goldstone-boson-exchange constituent quark model are found in remarkably
good agreement with existing experimental data.Comment: LATEX, 10 pages, including 4 ps-figures, slightly modified, one
additional referenc
Covariant axial form factor of the nucleon in a chiral constituent quark model
The axial form factor G_A of the nucleon is investigated for the
Goldstone-boson-exchange constituent quark model using the point-form approach
to relativistic quantum mechanics. The results, being covariant, show large
contributions from relativistic boost effects. The predictions are obtained
directly from the quark-model wave functions, without any further input such as
vertex or constituent-quark form factors, and fall remarkably close to the
available experimental data.Comment: 10 pages, 1 figure in .eps format, typeset with Elsevier elsart style
files included. Revised version with a newly added section about discussion
of results. To appear in Phys. Lett.
- âŠ