Ken Kawarabayashi

The η problem in the large-N limit: Effective Lagrangian approach

Abstract The effective lagrangian for the U(1) problem is reanalysed on the basis of the color gauge invariance of the underlying QCD. The decoupling mechanism of the axial-vector ghost from the physical sector is investigated with a particular gauge-fixing condition. The model is then extended to incorporate flavor degrees of freedom. It is explicitly demonstrated that the suppression mechanism for η →3 π is evaded in a manner consistent with anomalous Ward-Takahashi identities for the U(1) current without massless Nambu-Goldstone boson. The decays of ϑ → η ( η ′) γ are also estimated under the assumption that the decay in question dominantly proceeds through 2 gluons+γ with 2 gluons in the 1 S 0 state. Finally, strong CP violation is briefly discussed.

On the Partial Conservation of the U(1) Current

Recently proposed partial conservation of the UO) current (PCU,C) is applied to estimate the decay rates of various OZI forbidden processes. The results obtained are in good agreement with experiments and thus indicate the important role played by the UO) axial-vector anomaly in these decay processes. Octet jP = } + baryons are next introduced into this scheme and low energy theorems related to the B dependence of the matrix elements are investigated. Physical consequences of non-zero B (strong CP-violation) are also discussed with the help of the PCU,c. The results are used to give the bound on B.

Yukawa couplings in meson-soliton scattering

Abstract We study the meson-soliton scattering in the two-dimensional o 4 theory. We find that the t -matrix obtained from the linearized equation for the quantum fluctuation part of the meson field contains pole terms. We prove that the pole terms should be interpreted as the Born contributions to the t -matrix. The Yukawa interaction manifests itself as the Born term in the scattering amplitude, its strength being dictated by the classical solution.

A new scheme of ηand η′ mixing and violations of the OZI rule

Abstract A possible mixing scheme for η and η′ is proposed based on the picture that 0 − mesons form an ideal nonet in the dual planar theory and deviate from it through nonplanar diagrams. Using the new mixing angles (θ η ≠θ η′ ), we calculate radiative decay widths and production ratio of η and η′ which are then compared with experiments. Extension of our scheme to SU(4) leads to rather large violations of the OZI rule in decays of new particles with η or η′ in the final states.

A Model of Baryons Based on Duality and Unitarity

Abstract A model of “planar” baryons with (10 + 8) ↔ (1 + 8) exchange degeneracy is proposed, based on duality and unitarity. Dynamical mechanisms for deviation from the “planar” baryons are considered and the consequent pattern of broken exchange degenerate trajectories is compared with observed baryon spectra. Our model suggests a string picture of linear molecule type for baryons.

Modification of Adler's Neutrino Sum Rule Due to Second Class Current

We show that Adlers sum rule for inelastic neutrino scattering gets modified in a specific manner if second class axial vector current is present. The consequences of the altered sum rule which no more predicts scaling ar~ discussed and it is pointed out that this sum rule may offer the best testing ground for such currents.

Electromagnetic Structure of the Nucleon. II Upper Limits for Contributions from the Three-Pion State

Contributions to the isoscalar electromagnetic form factors from the three-pion state in the physical region of nucleon pair annihilation process are estimated by including the effects of pion correlations. The upper limits imposed on the contributions by the unitarity condition are also discussed numerically. It is shown that the results of the perturbatlon theory for those contributions that give rise to a considerable amount of the magnitude of the charge mean-square radius, are greatly modified and become negligibly small when the pion correlations are correctly taken into account. The unitarity condition, on the other hand, is shown to impose, in effect, no restriction on the three- pion state contribution from the physical region. (auth)

Decay rates of the Ω-meson and γ-3π interaction

SummaryRelations among various effective coupling constants, involved in the decay processes of the co and p mesons, are studied in connection with an attempt to estimate the strength of γ — ɛπ interaction. The amplitudeH, which characterizes the strength of γ -ɛπ interaction, is shown to be by a factor 2 or 3 smaller than the result calculated by perturbation theory in order to reproduce the observed decay rate of the neutral pion. Rates of rare decay modes of the co and p mesons are calculated explicitly in terms of the decay rate of the process Ω→π++π-+ & #x03C0;0. It is pointed out that the two-peak structure of the process ρ0→π++π- observed in the nucleon pair annihilation can be explained by the rare decay mode Ω→π++π-, if the width of the process Ω→ɛπ turns out to be smaller than 1 MeV. In this case the process ρρ ɛπ is possible to compete with the process Ω→ ɛπ.RiassuntoIn relazione ad un tentativo di valutare la forza dell‘interazione π-ɛπ, si sono studiati i rapporti fra varie costanti di accoppiamento effettive, coinvolte nei processi di decadimento dei mesoni Ω e ρ. Si mostra che l‘ampiezzaH, che caratterizza la forza dell‘interazione π-ɛπ, deve essere minore di un fattore 2 o 3 dei risultati dalla teoria delle perturbazioni, per dare i rapporti di decadimento osservati del pione neutro. Si calcolano esplicitamente i rapporti dei modi di decadimento rari dei mesoni Ω e ρ in funzione del rapporto di decadimento per il processo Ω→π++π-+π0. Si fa rilevare che la struttura a due picchi del processo ρ0→π++π- osservato nell‘annichilazione di coppie di nucleoni, si puÒ spiegare col raro modo di decadimento Ω→π++π-, se l‘ampiezza del processo Ω→ɛπ risulta minore di 1 MeV. In questo caso è possibile che il processo ρ→ɛπ competa col processo Ω→ɛπ.

Global Symmetry and the Branching Ratios for the K- Capture by the Nucleon

Branching ratios for the K- capture by the nucreon are studied to investigate the validity of Gell-Manns grobal symmetry. The following assumptions are made: (1) Gell-Manns grobar symmetry is valid, (2) K meson rs pseudoscalar, (3) mass differences among baryons can be neglected, and (4) processes involving K mesons are described by treating the coupling as perturbations in the lowest order that gives the effect. Under these assumptions, the matrix element for the processes are expressed in terms of the pi -N scattering matrix elements for which experimental data can be used. The branching ratios are compared with experimental results. (auth)

Isoscalar nucleon structure and multi-pion resonances

SummaryThe general features of the effects of multi-pion resonances on the isoscalar nucleon structure are investigated with a particular attention to the possible role of ρ and ω mesons. It is shown that the observed isoscalar charge structure of the nucleon can be accounted for in terms of the three-pion state contribution with a proper choice of ρ and Ω meson widths. A dependence of the calculated values on these resonance widths is also examined.RiassuntoSi studiano le caratteristiche generali degli effetti delle risonanze multipioniche sulla struttura isoscalare del nucleone, con particolare attenzione all’eventuale ruolo dei mesoni ρ ed Ω. Si dimostra che la struttura isoscalare della carica del nucleone, quale risulta dalle osservazioni, puÒ essere spiegata in base al oontributo dello stato a tre pioni, con una scelta opportuna delle ampiezze dei mesoni ρ ed Ω. Si studia anche la dipendenza dei valori calcolati da queste ampiezze di risonanza.