KNΛ and KNΣ coupling constants from the Chiral Bag Model

The KNΛ and KNΣ coupling constants have been calculated in the framework of the Chiral Bag Model(CBM). We find −3.88 ≤g _KNΛ≤−3.67 and 1.15 ≤g _KNΣ≤ 1.24 by taking into account pseudoscalar mesons (π, K) and vector mesons (ρ, ω, K ^*) field effects. Particularly, it is shown that vector mesons make significant contributions to the coupling constants g _KNΛ and g _KNΣ. Our values are existing within the experimental limits compared to the phenomenological values extracted from the kaon photoproduction and kaon-nucleon scattering experiments. Also, form factors are suggested for the πNN, πNΔ, KNΛ and KNΣ couplings. Received: 17 August 1998 / Revised version: 22 December 1998     

Testing of analyticity of the πN forward scattering amplitude and the determination of the πN coupling constant

We propose a new method for the testing of analyticity. Instead of using dispersion relations with traditional uncertainties in estimating the errors of the principal value integrals we work with a suitably defined set of moments.As an example we discuss the pion-nucleon CEX forward amplitude. The results indicate that the errors of the phase shift analysis used should probably be increased by a factor of two. Taking this into account we calculate the pion-nucleon coupling constant by analytic extrapolation and we find f² = 0.0835 ± 0.0040.     

Charge Splitting in πNΔ Form Factor

Physics of Atomic Nuclei - Experimental data on πN scattering in the elastic energy region w ≤ 1.45 GeV are analyzed within the K-matrix approach with effective lagrangians. The charge...     

The Chiral and Angular Momentum Content of the ρ-Meson

It is possible to define and calculate in a gauge-invariant manner the chiral as well as the partial wave content of the quark–antiquark Fock component of a meson in the infrared, where mass is generated. Using the variational method and a set of interpolators that span a complete chiral basis we extract in a lattice QCD Monte Carlo simulation with n _f = 2 dynamical light quarks the orbital angular momentum and spin content of the ρ-meson. We obtain in the infrared a simple ³ S ₁ component as a leading component of the ρ-meson with a small admixture of the ³ D ₁ partial wave, in agreement with the SU(6) flavor–spin symmetry.     

A study in the coupled πNN-NN system and the question of dinucleon resonances

Conclusions We have presented soms of our preliminary results on the coupled NN-NN problem. The overall result obtained so far is rather encouraging and we are currently making the model more sophisticated in order to be able to make more quantitative arguments which may hopefully serve somehow to clarify the dibaryon resonance problems. To end we would like to emphasize that since all the channels (viz.d d, d NN, NN NN, etc.) are unitarily coupled, one cannot arbitrarily change some input parameters to attain a better fit in one of the channels alone: all the channels are closely linked, which serves as a very strong constraint to the input. In near future we wish to extend our model to calculate processes with three-body final statesWork supported in part by Bundesministerium für Forschung und Technologie.Invited talk at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.I am grateful to my collaborators, Y. Avishai, C. Fayard, G. -H. Lamot and S. Nahabetian for numerous discussions.     

The homogeneous Lorentz group and πN charge-exchange scattering

The partial wave expansion of the scattering amplitudes in terms of the homogeneous Lorentz group extended to t ≠ 0 is studied with particular reference to the high-energy behaviour of πN charge-exchange scattering. In order that the analysis accomodate all the nice features of Regge pole theory, we find that it is necessary either that the ϱ-meson trajectory should contain both j_o = 0 and j_o = 1 contributions (a j_o-mixing) or that there exist another trajectory ϱ′ with the same quantum numbers as ϱ.     

The real part of the non-flip amplitude in πN charge exchange scattering

We evaluate the real non-flip amplitude for πN charge exchange from high energy polarization data and also from phase shift analyses. The implications of this evaluation for current high energy models is noted.     

The π-electron spectra of the benzene N-heterocyclics

The π-electron spectra of the nitrogen heterocyclics are discussed on the basis of a perturbation applied to the spectra of the corresponding aromatic hydrocarbons. The frequency of the first π→π band in pyridine is the same as that of the corresponding band in benzene, because of the accidental cancellation of a first-order blue shift by a second-order red shift. The first-and second-order shifts are related to two perturbation parameters, and these are obtained from experiment by examining the spectra of the benzene heterocyclics. These parameters can then be satisfactorily related to one another by assuming a perturbation field of the form exp (?2ηr)/r and by allowing for the C-N bond being shorter than the C-C bond in benzene.     

Peripherality and πN scattering

πN amplitudes, as far as they have been deduced, are used with an absorbed Reggeon exchange model to obtain amplitudes at larger −t with specified phases. Thus, satisfactory peripheral amplitudes are found. The phase behavior of the diffraction amplitude is discussed.     

A new interpretation of the πN σ-term

An explicit relation between the σ-term, the S-wave πN scattering length a⁽⁺⁾ and the range parameter b⁽⁺⁾ is established. The range term is shown to be the dominant feature. The important P-wave background terms in the extrapolation of the physical amplitude to the Cheng-Dashen point are shown to be very small if a path v²+2mv_B≅0, i.e., with cos θ≅0, is chosen. This avoids the compensating cancellations between large numbers typical of other procedures. Correction terms are also shown to be small using physical arguments. The present relation is in a convenient form for phenomenological applications.     

On the current status of OZI violation in πN and pp reactions

The available data on ω and φ production from πN and pp collisions are reanalyzed with respect to an OZI rule violation on the basis of transition matrix elements. The data are found to be compatible with a constant ratio R , which however, deviates substantially from the SU(3) prediction based on the present knowledge of the φ-ω mixing angle. Received: 5 July 1999 / Revised version: 20 October 1999     

Investigation of the I = 2 ϱπ system in πN → h̊ov;πN

The I = 2 ϱπ system produced in the reaction π⁻n → ϱ⁻ π⁻ p is investigated within the framework of the Reggeized charge exchange Deck mechanism. The diagram in which a π and ϱ are exchanged gives rise to an enhancement in the ϱπ effective mass at 1.1 GeV which is nearly independent of beam energy. Experimental evidence for such a state in π⁻n → ϱ⁻π⁻p, and in the related processes π⁺n → ϱ⁰π⁰p and π⁻p → ϱ⁻π⁻Δ⁺⁺ is discussed. The interpretation of this enhancement as an exotic state on the basis of the duality argument made by Chew and Pignotti is considered.     

The πN→ηN Reactions near Threshold and η-N Scatterings

The N^*(1535) model is proposed for pionic η- production reactions.The πN→ηN reaction cross sections near threshold and the S-wave η-N scattering length are calculated and compared with the experimental data and other theoretical calculations.     

τ− → π−π0ντ and e+e− → π+π− Processes in the Chiral Nambu—Jona-Lasinio Model Including the Interaction of Pions in the Final State

JETP Letters - The τ− → π−π0ντ and e+e− → π+π− processes have been described within the chiral Nambu—Jona-Lasinio model...     

The preparation,crystallography, and magnetic properties of the LixCo(1−x)O system

The Li_xCo(_1−x)O system has been prepared by the solid-state reaction between Li₂O₂ and CoO at 900°C. The material is a single-phase structure in the composition range 0 < x < 0.2, the lattice parameter of the cubic unit cell decreasing with increasing lithium content. At the composition x = 0.5 (i.e. LiCoO₂) a rhombohedral structure is formed. A phase diagram for this system has been developed.The crystal structure of material in the composition range 0 < x < 0.2 has been studied both above and below the antiferromagnetic Curie temperature. Both the antiferromagnetic Curie temperature and the related cubic-tetragonal transformation are found to occur at decreasing temperatures with increasing lithium content. In addition the magnitude of the crystallographic deformation decreases and finally vanishes with increasing lithium content.The magnetic-susceptibility data indicate that the magnetic moment of Co⁺² is best understood if the multiplet splitting is small compared to kT. Further, the moment of Co⁺³ is shown to be lowered by crystalline field effects. No effects attributable to the double exchange coupling were found. The absence of such a coupling is understood by consideration of the mechanism of electron transfer in the lithium-substituted compounds.