Contributions of γd → πNN + π0 d channels to the spin asymmetry and the Gerasimov-Drell-Hearn integral for the deuteron

Contributions from the semi-exclusive channels γd → π^± NN + π⁰ d and γd → π⁰ X (X=pn or d) to the deuteron spin asymmetry and the Gerasimov-Drell-Hearn (GDH) integral are explicitly evaluated using an enhanced elementary pion photoproduction operator and a realistic, high-precision potential model for the deuteron wave function. The sensitivity of the results to the elementary pion photoproduction operator is also investigated and considerable dependence is found. Results for the deuteron GDH integral are compared with the measurements from A2 and GDH@MAMI Collaborations.     

A generalization of Haldane's state-counting procedure and π-deformations of statistics

We consider the generalization of Haldane's state-counting procedure to describe all possible types of exclusion statistics which are linear in the deformation parameter g. The statistics are parametrized by elements of the symmetric group of the particles in question. For several specific cases we determine the form of the distribution functions which generalizes results obtained by Wu. Using them we analyze the low-temperature behavior and thermodynamic properties of these systems and compare our results with previous studies of the thermodynamics of a gas of g-ons. Various possible physical applications of these constructions are discussed.     

On Integration of the Nonlinear d’Alembert-Eikonal System and Conditional Symmetry of Nonlinear Wave Equations

Abstract

We study integrability of a system of nonlinear partial differential equations consisting of the nonlinear d’Alembert equation □u = F (u) and nonlinear eikonal equation u _xµ u _x µ = G(u) in the complex Minkowski space R(1, 3). A method suggested makes it possible to establish necessary and sufficient compatibility conditions and construct a general solution of the d’Alembert-eikonal system for all cases when it is compatible. The results obtained can be applied, in particular, to construct principally new (non-Lie, non-similarity) solutions of the non-linear d’Alembert, Dirac, and Yang-Mills equations. Solutions found in this way are shown to correspond to conditional symmetry of the equations enumerated above. Using the said approach, we study in detail conditional symmetry of the nonlinear wave equation □w = F ₀(w) in the four-dimensional Minkowski space. A number of new (non-Lie) reductions of the above equation are obtained giving rise to its new exact solutions which contain arbitrary functions.     

Ultra-violet absorption spectra and π-electron structures of nitromethane and the nitromethyl anion

The ultra-violet absorption spectrum of nitromethane was measured under various conditions. Besides the weak band at 270 mμ, a strong band, which may be regarded as due to the longest wavelength π→π* transition band, was observed at 198 mμ in the gaseous state. Further, the absorption spectrum of nitromethane was measured in aqueous solutions with several different ph values, and a strong band was observed at 233 mμ. From the fact that the pK_a value evaluated on the basis of the ph dependence of the absorption intensity is equal to that obtained electrometrically, it was concluded that the 233 mμ band is to be ascribed to the nitromethyl anion (H₂C^-NO₂). This band was found to shift to 238 mμ in alcoholic KOH solution.

The π-electron structure of the anion was studied theoretically by taking into account configuration interaction in terms of the ground, charge transfer, and locally excited configurations. It is shown that the 233 mμ band of the anion may be interpreted as an intramolecular charge-transfer absorption involving a large electron transfer from CH₂ ^- toward NO₂. It is suggested that electron donating substituent groups like NH₂, OH, and CH₂ ^- should cause the 198 mμ band of the nitro group to shift toward shorter wavelengths, in marked contrast to the case of substituted benzene molecules like aniline and phenol.     

Absorption and emission properties of phenylene ethynylene oligomers: effect of substitution and π-conjugation length

The optical properties of a series of π-conjugated phenylene-ethynylene oligomers (OPEs) have been studied by advanced quantum chemical methods. The ground state and lowest singlet excited state geometries of unsubstituted and different electron donor and acceptor groups substituted OPEs are optimized by density functional theory and configuration interaction singles methods. The absorption and emission spectra of unsubstituted and substituted OPEs have been calculated using the time-dependent density functional theory (TDDFT) method. The results of theoretical calculations are in good agreement with the available experimental results. It has been found that the substitution of electron donating and withdrawing groups in the phenyl ring and conjugation length of the OPEs has significantly affect both the absorption and emission spectra     

Models of πNN interactions

A NN model inspired by Quantum Chromodynamics is presented. The model gives an accurate fit to the most recent Arndt NN phase shifts up to 1 GeV and can be applied to study intermediate- and high-energy nuclear reactions.Invited talk to the symposium Mesons and Light Nuclei IV, Bechyn, Czechoslovakia, September 5–10, 1988.This work is supported by the U.S. Department of Energy, Nuclear Physics Division, under contract W-31-109-ENG-38.     

Structure of π- and 2π-Walls in Smectic films

The structure of ??- and 2??-walls in smectic films was reconstructed from optical reflectivity measurements. Investigations were made in free standing films of nonpolar Smectic-C and ferroelectric Smectic-C* liquid crystals. ??-walls are observed in magnetic field and 2??-walls in electric field parallel to the film plane. For the first time the distribution of molecular orientation across the walls was determined. Peculiarities of the wall structure related to the anisotropy of the film elasticity were found. The structure of the walls is well described by the theory taking into account the anisotropy of two-dimensional elasticity of smectic films.     

Characteristics of π−,\bar p,and antinuclei frompp collisions

An investigation of inclusivepp→π^?+? in terms of the covariant Boltzmann factor (BF) including the chemical potential μ indicates a) that the temperatureT increases less rapidly than expected from Stefan's law, b) that a scaling property holds for the fibreball velocity of π^? secondaries, leading to a multiplicity law like ～E _cm ^1/2 at high energy, and c) that μ_π is related to the quark mass: μ_π=2m _q ?m _π the quark massm _q determined by \(T_{\pi ^ - } \) at \(\bar pp\) threshold beingm _q =3T_π?330 MeV. Because ofthreshold effects \(T_{\bar p}< T_{\pi ^ - } \) , whereas \({{\mu _p } \mathord{\left/ {\vphantom {{\mu _p } {\mu _{\pi ^ - } }}} \right. \kern-0em} {\mu _{\pi ^ - } }} \simeq {3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-0em} 2}\) as expected from the quark contents of \(\bar p\) and π. The antinuclei \(\bar d\) and \({{\bar t} \mathord{\left/ {\vphantom {{\bar t} {\overline {He^3 } }}} \right. \kern-0em} {\overline {He^3 } }}\) observed inpp events are formed by coalescence of \(\bar p\) and \(\bar n\) produced in thepp collision. Semi-empirical formulae are proposed to estimate multiplicities of π^?, \(\bar p\) and antinuclei.     

Kinetic energy of π− p-atoms in liquid and gaseous hydrogen

We have measured the Doppler broadening of neutron time-of-flight spectra from the reaction π⁻ p → π⁰ + n in atomic states. From the data, we infer that the kinetic energy distribution of π⁻ p-atoms in liquid and gaseous hydrogen contains discrete ‘high-energy’ components with energies as high as 200 eV attributed to Coulomb de-excitation. In liquid hydrogen, evidence for Coulomb de-excitation transitions with Δn = 2 has been found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Role of t-channel meson exchanges in S-wave πN and KN scatterings

The low-energy S-wave πN and KN scatterings are studied by using the K-matrix approach within the meson exchange framework.The t-channel meson exchanges,especially ρ and σ exchanges,are found to play a very important role in these two processes.The t-channel ρ exchange determines the isospin structure of the scattering amplitudes,it gives attractive force in the low isospin state but repulsive force in the high isospin state.The t-channel σ exchange gives a very large contribution in these two processes,while it is negligible in meson-meson S-wave scatterings.     

Electroproduction of π0 mesons on the deuteron and neutral weak currents

An investigation is made into P-odd effects due to neutral weak currents in the process of electroproduction of ⁰ mesons on the deuteron, e^–+d e^–+⁰+d. The general structure of the differential cross section of this reaction (with allowance for the interference between the amplitudes of the electromagnetic and weak mechanisms) is obtained for the experimental conditions when the scattered electron and ⁰ meson are detected in the final state.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 17–21, September, 1980.     

The threshold photoproduction of π0 on nucleons and on few-nucleon systems

The absolute value of the π⁰ photoproduction cross section on the proton recently measured near threshold enables to reanalyze previous data collected on ²H, ³He, and ⁴He relatively to the proton. Absolute cross sections are presented for these nuclei in the energy region extending up to 10 MeV above threshold. The threshold s-wave amplitudes for ²H and ³He thus obtained are discussed in relation with the neutron threshold amplitude E^(nπ0)₀₊ value.     

The Chiral Bag Model and properties of the πNΔ system

The effective Hamiltonian for theN system is proposed in the framework of the Chiral Bag Model (CBM). The taking into account of gluonic and pionic correctinos to the pion-nucleon coupling constantg _N and the-decay axial constantg _A leads tog _N 13·5,g _A 1·28 which are in good agreement with experimental data.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.I wish to thank Gulamov K. G., Shelest V. P. and Zinoviev G. M. for useful discussions.     

The π+ d → pp reaction at intermediate energies

Conclusion The joint efforts of the laboratories with intermediate energies accelerators at ANL, KEK, LANL, LNPI, Saclay, SIN and TRIUMF produced a rather definite picture of the ⁺pp reaction in the isobar region. However the problem of anomalies for the square-root branch point due to the production of isobar in the intermediate state have not been resolved so far. The poles obtained in different phenomenological analyses could be just the effective parametrization of these cuts (see e.g. [13]). Anyway, some singularities are definitely necessary to describe the data.The experimental data in regions s < 2·05 GeV and s < 2·25 GeV are clearly insufficient. Further accumulation of the data in these regions is necessary. Polarized deuteron data are badly needed in the whole kinematical range [13]. Besides as it was mentioned before it is necessary to measure accurately cross sections of other inelastic reactions which are important for the investigation (observation?) of dibaryonsNN N, NN andd N, NN [21]. It would be of interest also to measure cross sections of non quasi two-particle channels likeNN N, 2N andd N, 2N [22]. (In the case ofNN scattering quasi two-particle channels are known to dominate in a wide energy range.)Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.I am grateful to L. A. Kondratyuk, M. G. Ryskin and M. I. Strikman for valuable discussions of the considered problems.     

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