1,184 research outputs found
Point form relativistic quantum mechanics and relativistic SU(6)
The point form is used as a framework for formulating a relativistic quantum mechanics, with the mass operator carrying the interactions of underlying constituents. A symplectic Lie algebra of mass operators is introduced from which a relativistic harmonic oscillator mass operator is formed. Mass splittings within the degenerate harmonic oscillator levels arise from relativistically invariant spin-spin, spin-orbit, and tensor mass operators. Internal flavor (and color) symmetries are introduced which make it possible to formulate a relativistic SU(6) model of baryons (and mesons). Careful attention is paid to the permutation symmetry properties of the hadronic wave functions, which are written as polynomials in Bargmann spaces
Bakamjian-Thomas mass operator for the few-nucleon system from chiral dynamics
We present an exploratory study consisting in the formulation of a
relativistic quantum mechanics to describe the few-nucleon system at low
energy, starting from the quantum field theoretical chiral Lagrangian involving
pions and nucleons. To this aim we construct a Bakamjian-Thomas mass operator
and perform a truncation of the Fock space which respects at each stage the
relativistic covariance. Such truncation is justified, at sufficiently low
energy, in the framework of a systematic chiral expansion. As an illustration
we discuss the bound state observables and low-energy phaseshifts of the
nucleon-nucleon and pion-nucleon scattering at the leading order of our scheme.Comment: 17 pages, 10 figures. Revised formulation, matches the journal
versio
A relativistic coupled-channel formalism for the pion form factor
The electromagnetic form factor of a confined quark-antiquark pair is
calculated within the framework of point-form relativistic quantum mechanics.
The dynamics of theexchanged photon is explicitly taken into account by
treating theelectromagnetic scattering of an electron by a meson as a
relativistic two-channel problem for a Bakamjian-Thomas type mass operator.
This approach guarantees Poincare invariance. Using a Feshbach reduction the
coupled-channel problem can be converted into a one-channel problem for the
elastic electron-meson channel. By comparing the one-photon-exchange optical
potential at the constituent and hadronic levels, we are able to unambiguously
identify the electromagnetic meson form factor. Violations of
cluster-separability properties, which are inherent in the Bakamjian-Thomas
approach, become negligible for sufficiently large invariant mass of the
electron-meson system. In the limit of an infinitely large invariant mass, an
equivalence with form-factor calculations done in front-form relativistic
quantum mechanics is established analytically.Comment: 3 pages, 1 figure, submitted to EPJ Web of Conference
Point-form quantum field theory and meson form factors
We shortly review point-form quantum field theory, i.e. the canonical
quantization of a relativistic field theory on a Lorentz-invariant surface of
the form . As an example of how point-form quantum field
theory may enter the framework of relativistic quantum mechanics we discuss the
calculation of the electromagnetic form factor of a confined quark-antiquark
pair (e.g. the pion).Comment: 3 pages, 2 figures. Based on a talk presented by W. Schweiger at the
20th European Conference on Few-Body Problems in Physics, September 10-14
2007, Pisa, Ital
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
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