arXiv subjects
Publications and source records attributed to H. J. Weber.
Chiral spin fraction models agree with the proton spin data only when the chiral quark-Goldstone boson couplings are pure spinflip. For axial-vector coupling from soft-pion physics this is true for massless quarks but not for constituent quarks. Axial-vector quark-Goldstone boson couplings with {\bf constituent} quarks are found to be inconsistent with the proton spin data.
We compare the Bakamjian-Thomas (BT) formulation of relativistic few-body systems with light front field theories that maintain closer contact with Feynman diagrams. We find that Feynman diagrams distinguish Melosh rotations and other kinematical quantities belonging to various composite subsystem frames that correspond to different loop integrals. The BT formalism knows only the rest frame of the whole composite system, where everything is evaluated.
Starting from the standard and commonly used relativistic nucleon wave function, we show that residual interactions based on gluon or Goldstone boson exchanges generate additional components leading to configuration mixing. This result suggests that realistic nucleon wave functions can be expected to be far more complex than seemingly successful form factor fits in relativistic quark models would have one believe.
The spin fractions and deep inelastic structure functions of the proton are analyzed using chiral field theory involving Goldstone bosons. A detailed comparison with recent chiral models sheds light on their successful description of the spin fractions of the proton as being due to neglecting helicity non-flip chiral transitions. This approximation is valid for zero mass quarks but not for constituent quarks. Since the chiral spin fraction models with the pure spin-flip approximation reproduce the measured spin fractions of the proton, axialvector constituent-quark-Goldstone boson coupling is found to be inconsistent with the proton spin data. Initial quark valence distributions are then constructed using quark counting constraints at Bjorken $x \to 1$ and Regge behavior at $x \to 0$. Sea quark distributions predicted by chiral field theory on this basis have correct order of magnitude and shape. The spin fractions agree with the data.
Orthonormal spin-flavor wave functions of Lorentz covariant quark models of the Bakamjian-Thomas type are constructed for nucleon resonances. Three different bases are presented. The manifestly Lorentz covariant Dirac-Melosh basis is related to the Pauli-Melosh basis and the symmetrized Bargmann-Wigner basis that are manifestly orthogonal.
The SU(3) symmetric chiral quark model, which describes interactions between quarks, gluons and the Goldstone bosons, explains reasonably well many aspects of the flavor and spin structure of the proton, except for the values of $f_3/f_8$ and $Δ_3/Δ_8$. Introducing the SU(3)-breaking effect suggested by the mass difference between the strange and nonstrange quarks, we find that this discrepancy can be removed and better overall agreement obtained.
A constituent quark model is developed for an arbitrary light- cone direction ω. Form factors are obtained from free one-body electromagnetic current matrix elements. They are found to be ω- independent for spin-0 mesons, the nucleon and Λhyperon, while there is ω-dependence for spin-1 systems like the deuteron.
A loop expansion is implemented based on the path integral quantization of the light-cone $ϕ^4$ field theory in 1+1 dimensions. The effective potential as a function of the zero-mode field $ω$ is calculated up to two loop order and its derivative with respect to $ω$ is used to determine the vacuum expectation value of the field $ϕ$. The critical coupling constant at the spontaneous symmetry breakdown is consistent with that obtained in the ordinary instant-form field theory. The critical exponents which describe the behavior of the susceptibility and the vacuum expectation value of $ϕ$ near the critical point are evaluated from the effective potential. The one loop diagrams for the connected Green's function are calculated in momentum space. The relevant equal-time correlation function is shown to be closely related.
Spin-flavor fractions of quarks in the proton and several hyperons are obtained from their lowest order chiral fluctuations involving Goldstone bosons. SU(3) flavor breaking, relativistic effects and the axial anomaly are included. The validity of the Karl-Sehgal formulas for magnetic moments is studied as well.
The spin and flavor fractions of constituent quarks in the proton are obtained from their chiral fluctuations involving Goldstone bosons. SU(3) flavor symmetry breaking suggested by the mass difference between the strange and up, down quarks is included, and this improves the agreement with the data markedly.
Deep inelastic structure functions for the nucleon are obtained in a constituent quark model on the light cone. In the Bjorken limit the parton model is derived. Structure functions from the hadronic tensor at the scale $μ\sim 0.25$ GeV are evolved from (0.6 GeV$)^{2}$ to $-q^{2}\sim 15$ GeV$^{2}$. The model incorporates the quark boosts, is designed to describe form factors and structure functions, and to provide a link between the parton and constituent quark models. The main effect of the spin force between quarks is described in terms of smaller (and lighter) scalar $u-d$ quark pairs in the nucleon. To account for the negative slope of $F^{n}_{2}(x)/F^{p}_{2}(x)$, attraction between scalar $u-d$ quark pairs and incorporation of boosts are required. The two-body spin force between quarks from color magnetism also leads to a negative slope. The polarization asymmetry $A^{p}_{1}$ is in fair agreement with the EMC data in the valence quark region. Revised hep-ph/9401342, Phys. Rev. D.
Deep inelastic structure functions for the nucleon are obtained in a constituent quark model on the light cone. Parton model formulas are derived. The negative slope of $F_{2}^{n}/F_{2}^{p} requires attraction between scalar quark pairs. Color magnetism leads to a positive slope. 6 Figures are available from author. Typeset in REVTEX.