Meson-baryon Coupling Constants Research Articles

Meson exchanges in the harmonic-oscillator quark model

Meson exchanges are introduced into the harmonic oscillator quark model along with a lower quark wave function. The mechanism is based on quark correlations that derive from quark exchange scattering via gluon exchange at short distances. This method allows avoiding spurious van der Waals forces at long range. Meson-baryon coupling constants and vertex form factors are calculated. They are found to be in agreement with those obtained from other quark models, phenomenological potentials, and the broken SU(3) flavor symmetry. The resulting $S$-wave NN phase shifts are compared with those from quark-molecular models.NUCLEAR REACTIONS Meson exchanges, ${E}_{\mathrm{lab}}\ensuremath{\le}300$ MeV. Coupling constants, vertex form factors calculated from harmonic-oscillator quark interchange model. Comparison of NN $S$-wave phase shifts with those of potential models.

Radiative Corrections to Pion-Nucleon Coupling Constants

We formulate a renormalization procedure for avoiding the problem of electromagnetic divergences in second-order electromagnetic amplitudes. We apply it to evaluate radiative corrections to pion-nucleon coupling constants. Such corrections are essentially divided into two categories: "low momentum" to ordinary minimal-coupling expressions and "tadpole" corrections originating from the high-momentum part of the photon integral. The first part is calculated using a Cottingham procedure, weak partial conservation of axial-vector current (PCAC), and saturation by low-lying intermediate states. The tadpole contribution is related to the analogous one in the case of electromagnetic mass shifts and is parametrized in terms of the ratio $\frac{{C}_{3}}{{C}_{8}}$ between tadpole-electromagnetic and medium-strong interactions and of the deviations from S${\mathrm{U}}_{3}$ symmetry for meson-baryon coupling constants. The corrections to the pion-nucleon coupling constants due to electromagnetic mass shifts are estimated separately.

“Bootstrap” sum rules for baryon-baryon scattering amplitudes

“Bootstrap” sum rules have been analysed for NN, ΞΞ, ΣΣ and ΛΛ scattering amplitudes. Coupling constants of the non-strange mesons with 1 2 + baryons have been determined. Mass relations μ B 2 ≃ m Σ 2; μ A 1 2 ≃ m Σ 2 have been obtained. The dependence of pseudoscalar meson-baryon coupling constants on the hypercharge has been found.

First-OrderSU3Corrections to Meson-Baryon Coupling Constants

Regge theory and some aspects of duality are used in order to parametrize the meson-baryon coupling constants, including first-order $S{U}_{3}$-breaking effects. Five of the more relevant coupling constants are expressed in terms of three unknown constants, yielding two independent sum rules. An estimate of corrections due to $S{U}_{3}$ mass shifts is suggested.

Meson-Baryon Interactions with Baryons Belonging to the Nonlinear Representations of ChiralU(3)⊗U(3)

We derive a general chiral $U(3)\ensuremath{\bigotimes}U(3)$ phenomenological Lagrangian for the meson-baryon system. The meson-baryon derivative coupling is discussed in detail, and $K\ensuremath{-}N$ scattering is studied. Some renormalized meson-baryon coupling constants are computed and compared with experiments. A suitable canonical transformation is introduced, and conditions under which it yields the Yukawa coupling are discussed.

High-spin baryons in the cutkosky bootstrap model

We investigate the Cutkosky bootstrap equations for static meson-baryon scattering in the case of degenerate baryon masses. We consider first P-wave meson-baryon scattering and find that the symmetry group SU(2) S ⊗ O(3) K for the meson-baryon interaction suggested first by Golowich can be replaced by the group SU(2) J ⊗ SU(2) K . The quantum number S is identified with isospin I and so-called K-spin can have both integer and half-integer values. The reduced coupling constants are found to be non-vanishing only if the spin J can be obtained by vectorial addition of I and K as was assumed by Golowich from the beginning. As a consequence of the bootstrap equations it follows that the meson-baryon interaction is invariant under the group SU(2) I ⊗ SU(2) J ⊗ SU(2) K ⊗ U(1) Y° Using this fact, we obtain a solution for the meson-baryon coupling constants for scattering of arbitrary mesons in all partial waves on baryons with arbitrary parity and strangeness.

Calculations using the dispersion relations for forward K±p scattering

Using the dispersion relations for the K±p forward elastic scattering amplitudes, it is found that the combination of coupling constants (gK−pΛ2 + 0.847 gK−pΣO2) is 155±35. This result is compatible with the assumption of SU(3) invariance for the meson-baryon coupling constants.

The structure of the nucleon in bootstrap theory

On the basis of the self-consistency theory and the bootstrap dynamics the N →π + N form factor with one nucleon off the mass shell is calculated in the static model. It is shown that this form factor is an analytic function with analytic properties prescribed by the postulates of S-matrix theory. In addition to the correct analytic properties the form factor fulfils the unitarity condition if and only if certain relations among the meson-baryon coupling constants and among the masses of the baryons are fulfilled. The required ratios of coupling constants are the same as those derived by Chew and by Abers et al. in their static bootstrap model. Moreover the new condition for the mass of Δ-resonance is obtained here.

Dispersion Sum Rules for Nucleon-Antinucleon Scattering

Nucleon-antinucleon scattering is considered in order to derive two sum rules, which follow from the one-dimensional idispersion relations for a fixed momentum transfer, under some assumptions about the high-energy behavor of the invariant amplitudes. The sum rules give simple relations between the various meson-baryon coupling constants and the parameters required to characterize the deuteron. From one of the sum rules, the $\ensuremath{\omega}\ensuremath{-}\ensuremath{\varphi}$ mixing angle is estimated. The results are then briefly discussed.

Meson-Baryon Coupling Constants in a Current-Current Model

Methods recently developed by Chiu and Schechter for evaluation of matrix elements of bilinear products of hadron currents are combined with the PCAC (partially conserved axial-vector current) reduction technique to obtain approximate values of the meson-baryon coupling constants. Several current-current-type symmetry-breaking Hamiltonians are examined, and the results are compared with recent calculations using a Hamiltonian proportional to the space integral of the eighth component of the quark scalar density.

Evaluation of Meson-Baryon Coupling Constants from Current Divergences

Evaluation of Meson-Baryon Coupling Constants from Current Divergences

On the predictions of the algebra of currents and of a quark model about the meson-baryon coupling constants

On the predictions of the algebra of currents and of a quark model about the meson-baryon coupling constants

Evaluation of Meson-Baryon Coupling Constants from Current Divergences

In this note we examine how in broken $S{U}_{3}$ symmetry the strong coupling constants may be obtained in terms of the $\frac{d}{f}$ ratio of the weak axial-vector current and the physical baryon masses by making suitable assumptions, particularly the hypothesis of partially conserved axial-vector current and Cabibbo's assumptions about leptonic decays. Our derivation suggests that the correct starting point for calculations in broken $S{U}_{3}$ assigns the pseudovector couplings (rather than the pseudoscalar couplings) the values of the corresponding structure constants of the exact symmetry.

Meson-Baryon Coupling Constants in Broken SU(3) and the Algebra of Currents

Using the algebra of currents, we study the renormalization effects on the meson-baryon coupling constants, due to SU(3) breaking.

Some Simple Consequences ofSU(4)Symmetry

The electromagnetic properties of the nucleons and ${N}^{*}$, as well as the meson-baryon coupling constants, are examined within the framework of an $\mathrm{SU}(4)$ symmetry combining spin and isospin. The motivation is to examine the consequences of such a symmetry at low energies without having to worry about the large mass differences within the $\mathrm{SU}(3)$ multiplets in the corresponding $\mathrm{SU}(6)$ theory. The coupling-constant ratios are in qualitative agreement with the experimental values. The arbitrariness in the proton-neutron magnetic-moment ratio is discussed. In the model where the electromagnetic interaction of the baryons is mediated by the vector mesons in the adjoint representation of $\mathrm{SU}(4)$, the magnetic-moment ratios agree with the $\mathrm{SU}(6)$ results.

On the question ofCP-invariance and a possible difference of θv and θA in hyperon leptonic decays

A comparison of Cabibbo’s theory of weak interaction with the recently determined branching ratios for electronic hyperon decays is made, to investigate the influence of a possible CP- violating term (μ/2mB)σμvqvγ5 in the decay amplitudes on the accuracy of the determination of the axial vector angle θA. Using for the vector angle the experimental value θV = 0.214 ± 0.010, we obtain for the caseΜ = 0 an axial vector angle θV= 0.35 ± 0.03 being more than three standard deviations larger than θV. In the case of maximum CP violation there is again a possible solution with θA= θV for Re Μ= 0 and |Im Μ,| = 19 ± 6. An imaginary part of this order leads to an observable transversal λ-polarization in the decay Σ → λe-v. Thedjf mixing parameter ζ for the axial vector weak interaction is determined to be ζ = 0.68 ± 0.04. This is of the same order as the corresponding mixing parameter for strong pseudoscalar meson to baryon coupling. Finally generalized Goldberger-Treiman relations are used to derive numerical values for pseudoscalar mesonbaryon coupling constants.

Possible relations among the meson-baryon coupling constants

It is assumed that the strong interactions of the mesons and baryons can be described in terms of a Lagrangian containing at most eight coupling constants. A simple assumption is then made that only one magnitude g is required to describe all the pion-baryon couplings and that one magnitude f is sufficient to describe the couplings of the baryons to K-mesons. Within this restriction, there are 3 8 = 6561 ways to write down the Lagrangian, since each of the eight coupling constants may be positive, negative, or absent. It is shown that many of these possiblities lead to equivalent descriptions of the strong interactions, and that still other possibilities lead to predictions in contradiction to experiment. However, several hundred nonequivalent Lagrangians satisfying the assumptions are not eliminated by the arguments of this paper. Examination of a number of the remaining possibilities in fourthorder perturbation theory indicates that some of them are more likely than others, but none can be ruled out by the arguments given here.