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     

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 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.     

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.     

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 effect of fluorine substitutions on the refractive index properties for π-conjugated calamitic nematic materials

In order to reveal the effect of fluorine substitutions on the refractive index properties for calamitic nematic materials, we carried out a comparative study with respect to non-fluorinated and two types of laterally fluorinated 1,4-bis[4-(hexyloxy)phenyl]ethynylbenzene molecules. Phase transition behaviours were investigated by differential scanning calorimetry and polarised optical microscopy. Additionally, extraordinary and ordinary refractive index and birefringence were evaluated from each single component system. All the analogues exhibited high birefringence values beyond 0.3 at 550 nm, of which an analogue with a fluorine substitution at the central benzene ring showed the highest Δn-value of 0.43. With respect to an analogue with the highest level of fluorination, Δn as well as n_e and n_o values were declined due to decreased order parameter and diluted molecular density. Not only the mesomorphic behaviours but also optical properties strongly relied on the manner of fluorine substitution including the number and position.     

WKB properties of the time-dependent Schrödinger system

It is shown that the time-dependent WKB expansion highlights some of the hidden properties of the Schrödinger equation and forms a natural bridge between that equation and the functional integral formulation of quantum mechanics. In particular it is shown that the leading (zero- and first-order in ) terms in the WKB expansion are essentially classical, and the relationship of this result to the classical nature of the WKB partition function, and of the anomalies in quantum field theory, is discussed.     

Study of cohesive,electronic and magnetic properties of the Ni–In intermetallic system

Cohesive, electronic and magnetic properties of the intermetallic system Ni–In, specifically the stable phases Ni₃In-hP8, Ni₂In-hP6, NiIn-hP6 and Ni₂In₃-hP5, have been investigated. At present, these materials are of great interest in connection to the application of the In–Sn alloys as lead-free micro-soldering alloys, and considering Ni as the contact material. In spite of this, scarce literature regarding basic thermodynamic properties of the Ni–In intermetallic phases has been found. Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations is used. All the calculations include spin polarization. Structural parameters, formation energies and cohesive properties of the different phases are studied through minimization of internal parameters. The electronic density of states (DOS) is analyzed for each optimized structure. We found that the NiIn-hP6 phase is the most stable one and only the Ni₃In-hP8 phase exhibits magnetic properties.     

Novel spectrum properties of the periodic π-phase-shifted fiber Bragg grating

A special periodic π-phase-shifted (π-PS) fiber Bragg grating (FBG) is proposed to achieve multichannel reflections. The Fourier analysis and the simulations based on the transfer matrix method show that this simple structure can generate multichannel response with high reflectivity. The reflectivity is much greater than that of the traditional sampled FBG for the same value of κL. Therefore the length of the fiber or the amplitude of refractive index modulation can be greatly reduced if such a periodic π-PS FBG is used instead of the traditional sampled FBG in the applications of comb filtering and optical wavelength division multiplexing. Besides, when the duty cycle is 0.5, this periodic π-PS FBG can create dual wavelength spectrum with high reflectivity.     

Hyperpolarizabilities of Chiral Molecules Based on Three-Coupled-Oscillator Model

A chiral molecular model of three coupled oscillators is established. A set of coupling equations and hyperpolarizabilities for the chiral molecules with the tripod structure are presented. The expression of second-order nonlinear susceptibility is derived for an isotropic molecular system. The calculated hyperpolarizabilities o[ NPAN and NPP chiral molecules are consistent with the experimental results and the applicability of this model is validated.     

First-principles investigation of the elastic and electronic properties of the binary intermetallics in the Al–La alloy system

The structural, elastic and electronic properties of Al₂La, AlLa₃ and Al₃La binary intermetallics in the Al–La alloy system were investigated using the first-principles method. The calculated lattice constants were consistent with the experimental values. Formation enthalpy and cohesive energy showed that the studied Al₂La, AlLa₃ and Al₃La all have a higher structural stability, and the alloying ability of Al₂La and Al₃La is stronger than that of AlLa₃. The single-crystal elastic constants (C_ij) as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio υ and anisotropy value A) were calculated by the Voigt–Reuss–Hill (V–R–H) approximations, and the relationship of these elastic parameters between Al₂La, AlLa₃ and Al₃La phases were discussed in detail. The results showed that Al₂La and Al₃La which are anisotropic materials are absolutely brittle, while the isotropic AlLa₃ is slightly ductile. Finally, the electronic density of states (DOS) was also calculated to reveal the underlying mechanism of structural stability.     

The scaling reduction of the three-wave resonant system and the Painlevé VI equation

The scaling invariant solutions of the three-wave resonant system in one spatial and one temporal dimension satisfy a system of three first-order nonlinear ordinary differential equations. These equations can be reduced to one second-order equation quadratic in the second derivative. This equation is outside the class of equations classified by Painlevé and his school. However, it is a special case of an equation recently found to be related via a one-to-one transformation to the Painlevé VI equation.     

The Re-Analysis of the 1700 MeV Structure of the P 11 Partial Wave Using the πN → KΛ Production Data

We have used the Breit-Wigner resonance model with S ₁₁, P ₁₁, and P ₁₃ resonances in the s-channel to reanalyze the old πN → KΛ data with the aim to establish the origin of the prominent structure in the total cross section in the vicinity of 1700 MeV. We have found a new set of resonance parameters enforcing the experimentally observed structure of the total cross-section data simultaneously with the linear dependence of the differential cross sections with cos θ in the energy range 1650 MeV < W < 1800 MeV. Owing to the differential cross-section linearity, the P ₁₃ partial wave has been strongly attenuated in this model, and the total cross-section structure is attributed to the resonant behavior of the P ₁₁ partial wave. In this paper we show that, at least in the Breit-Wigner resonance model, it is not possible to achieve a detailed reproduction of the narrow 1700 MeV total cross-section peak using the standard partial widths. To understand the phenomenon, a much narrower width of a resonant state, the N(1710) P ₁₁ in our case, is required (Γ ≈ 68 MeV), but then the agreement of the model predictions with the total cross-section data at higher energies is lost. One way out is to allow for the existence of another P ₁₁ resonance in that energy range. The same feature is shown by the polarization data: The introduction of a much narrower resonance spoils the level of agreement which the Breit-Wigner resonance model is able to achieve with experiment, but the consistency is restored when another resonance is introduced. Analyzing the qqq or qqqq nature of the recommended narrow P ₁₁ structure in the neighborhood of 1700 MeV we reopen (remind of) the possibility that another P ₁₁ resonant state exists in addition to the standard N(1710) P ₁₁ PDG-resonance, and that one of the two states can be identified with the yet undiscovered cryptoexotic pentaquark state. To clarify the situation, we strongly recommend a remeasurement of the πN → KΛ process in the energy range 1650 MeV < W < 1800 MeV.     

Experimental study of π− π+ system at low invariant-masses

We report on results of an experiment to study the reaction ^– p ^{– +} in the incident pion momentum region between 295 and 450 MeV/c. A departure from phase space was observed in invariant-mass spectra and angular distributions which cannot be explained with and resonance production. It indicates aI=0,J ^P = 0^{+ – +} final-state interaction.Deceased     

Some Remarks on a Generalization of the Superintegrable Chiral Potts Model

The spontaneous magnetization of a two-dimensional lattice model can be expressed in terms of the partition function W of a system with fixed boundary spins and an extra weight dependent on the value of a particular central spin. For the superintegrable case of the chiral Potts model with cylindrical boundary conditions, W can be expressed in terms of reduced Hamiltonians H and a central spin operator S. We conjectured in a previous paper that W can be written as a determinant, similar to that of the Ising model. Here we generalize this conjecture to any Hamiltonians that satisfy a more general Onsager algebra, and give a conjecture for the elements of S.     

The N*(1710) as a resonance in the ππN system

We study the ππN system by solving the Faddeev equations, for which the input two-body t-matrices are obtained by solving the Bethe-Salpeter equation in the coupled-channel formalism. The potentials for the ππ, πN sub-systems and their coupled channels are obtained from chiral Lagrangians, which have been earlier used to study resonances in these systems successfully. In this work, we find a resonance in the ππN system with a mass of 1704 ? i375/2MeV and with quantum numbers I = 1/2, J ^π = 1/2⁺. We identify this state with the N ^*(1710). This peak is found where the energies of the ππ sub-system fall in the region of the σ-resonance. We do not find evidence for the Roper resonance in our study indicating a more complex structure for this resonance, nor for any state with total isospin I = 3/2 or 5/2.