689 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
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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
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