An isotropic cosmological model in general scalar tensor theory

An isotropic homogeneous cosmological model with Robertson-Walker line element is studied in general scalar tensor theory where the parameterω is a function of the scalar field. The model consists of perfect fluid with the equation of statep=ερ. Exact solutions are obtained in Dicke’s conformally transformed units forε=1 andε=1/3 assuming a functional relationship betweenω and the scalar fieldφ. The properties are compared with vacuum models in this theory.     

φ-meson photoproduction from nuclei

We study coherent and incoherent φ-meson photoproduction from nuclei. The available data are analyzed in terms of single- and coupled-channel photoproduction. It is found that the data on coherent photoproduction can be well reproduced within a single-channel optical model and show only little room for ω-φ mixing. These data indicate a normal distortion of the φ-meson in nuclei, which is compatible with the results obtained through the vector meson dominance model. The data on incoherent φ-meson photoproduction show an anomalous A-dependence resulting in a very strong φ-meson distortion. These data can be explained by a coupled-channel effect through the dominant contribution from the ω↦φ or the π↦φ transition or, more speculative, through the excitation of a cryptoexotic B _φ-baryon.     

Study of ω-meson production in pp collisions at ANKE

The production of ω-mesons in the pp → ppω reaction has been investigated with the COSY-ANKE spectrometer for excess energies of 60 and 92MeV by detecting the two final protons and reconstructing their missing mass. The large physical background was subtracted using an event-by-event transformation of the proton momenta between the two energies. Differential distributions and total cross-sections were obtained after careful studies of possible systematic uncertainties in the overall ANKE acceptance. The results are compared with the predictions of theoretical models. Combined with data on the φ-meson, a more refined estimate is made of the Okubo-Zweig-Iizuka rule violation in the φ/ω production ratio.     

Production of φ mesons in near-threshold πN and NN reactions

We analyze the production of φ mesons in πN and NN reactions in the near-threshold region, using throughout the conventional “non-strange” dynamics based on such processes which are allowed by the non-ideal ω-φ mixing. We show that the occurrence of the direct φNN interaction may show up in different unpolarized and polarization observables in πN→Nφ reactions. We find a strong non-trivial difference between observables in the reactions pp→ppφ and pn→pnφ caused by the different role of the spin singlet and triplet states in the entrance channel. A series of predictions for the experimental study of this effect is presented. Received: 27 January 2000     

Phase- and helicity-dependent effects in three-color ionization

We study the two-photon ionization of the hydrogen atom from its ground state by a three-color electromagnetic field consisting of a superposition of an IR laser and two of its consecutive odd harmonics of order 2p−1 and 2p+1, withp a positive integer and constant relative phase difference. The ionization process due to the net absorption of the energy 2pħω (ω being the IR laser frequency) is considered. The influence of phase difference and helicity on the azimuthal angular distribution of the ejected photoelectrons is illustrated in the case in which the two harmonics have identical polarizations. Phase effect on the alignment of the differential ionization rate is also investigated.     

New hadronic states observed at BES II

The report includes the new observation of X(1835) in J/ψ→γη ^′ π ⁺ π ^-, the ωφ threshold enhancement in J/ψ→γωφ, the ωω structure in J/ψ→γωω and the broad 1^- structure at the low K ⁺ K ^- invariant-mass spectrum in J/ψ→K ⁺ K ^- π ⁰.     

Matrix element effects inε 2 ω of the insulating perovskites

We report the calculation of matrix element effects in the frequency dependent dielectric function,ε ₂ ω, for insulatingd-band perovskites. Analytical expressions are obtained forε ₂ ω which yield results that are in good agreement with data for SrTiO₃. These results also provide a direct comparison betweenε ₂ ω and the joint density-of-states. The joint density-of-state approximation is found to be particularly poor due to unusually large transition matrix element effects. On leave from Middle East Technical University, Ankara, Turkey     

Quantum states with continuous spectrum for a general time-dependent oscillator

We investigated quantum states with continuous spectrum for a general time-dependent oscillator using invariant operator and unitary transformation methods together. The form of the transformed invariant operator by a unitary operator is the same as the Hamiltonian of the simple harmonic oscillator:I’ = p²/2 +ω ² q ²/2. The fact thatω ² of the transformed invariant operator is constant enabled us to investigate the system separately for three cases, whereω ² > 0,ω ² < 0, andω ² = 0. The eigenstates of the system are discrete forω ² > 0. On the other hand, forω ² <− 0, the eigenstates are continuous. The time-dependent oscillators whose spectra of the wave function are continuous are not oscillatory. The wave function forω ² < 0 is expressed in terms of the parabolic cylinder function. We applied our theory to the driven harmonic oscillator with strongly pulsating mass.     

(2γ,2e) total and differential cross-section calculations for helium with ?ω = 40–50 eV

We consider two-photon double ionization of helium and analyse the electron dynamics in the region where the process is direct (39.49 eV < ħω < 54.42 eV). The fundamental process of two-photon double ionization (TPDI) is far from being well understood. In order to gain physical insight into the dynamics involved in TPDI, we investigate the electron energy distributions for ħω = 46 eV and ħω = 50 eV, angular distributions are also analysed. The theoretical approach is based on the resolution of the time-dependent Schr?dinger equation (TDSE), using a spectral approach. At the end of the pulse the TPDI probability is extracted from the total wavefunction using two different approaches. The first one neglects the electron interaction in the double continuum while the second one includes electron correlation effects. At ħω ≈ 45 eV the electrons are preferably emitted back-to-back with equal energy. At ħω = 50 eV the excess energy is likely to be transfered to one of the electron, while the electrons are emitted in opposite or same directions.     

Cosmological models with constant deceleration parameter in Nordtvedt’s theory

Exact solutions of the field equations of Nordtvedt’s theory for spatially flat FRW models with constant deceleration parameter have been obtained. Singular solutions with (i) power-law (ii) exponential expansion have been studied in Nordtvedt’s theory where the coupling parameterω is a function of the scalar fieldφ.     

Recent KLOE results on hadron physics

The KLOE experiment at the Frascati e ⁺ e ^- collider DAFNE has completed this year its data taking. An integrated luminosity of 2.7fb^-1 has been collected mostly at the φ-resonance peak. A wide experimental program is in progress. The detection of φ radiative decays allows to study the properties of the lowest-mass scalar and pseudoscalar mesons and to obtain information on their structure. The main results are reviewed together with the prospects for low-energy e ⁺ e ^- physics at Frascati.     

Influence of the reagent vibration on the stereo-dynamics of the reactions D- + H2 and H- + D2

Employing the quasi-classical trajectory method and the potential energy surface of Panda and Sathyamurhy [Panda A N and Sathyamurthy N 2004 J. Chem. Phys. 121 9343], the effect of the reagent vibration on vector correlation of the ion-molecule reactions D^- + H₂ and H^- + D₂ is studied at a collision energy of 35.7 kcal/mol. Four generalized polarization-dependent differential cross sections (2π/σ)(dσ₀₀/dω_t),(2π/σ)(dσ₂₀/dω_t),(2π/σ)(dσ₂₂/dω_t), and (2π/σ)(dσ₂₀/dω_t) are presented in the centre-of-mass reference frame, separately. At the same time, the effects on the product angular distributions P(θ_r), P(φ_r) and P(θ_r,φ_r) of the title reactions are also analysed. The calculated results show that the scattering tendencies of the product HD, the alignment and the orientation of j' sensitively depend on reagent molecule vibration.     

Scaling in dispersion rheology

Summary A nonequilibrium fluid lattice model of concentrated colloidal dispersions is presented to predict the effects of the microstructure, particle interactions, volume fraction (ϕ), frequency (ω), and the longest viscoelastic relaxation time on the complex shear viscosity. In addition to the pair interactions between colloidal particles, the many-body interactions between the particles and the equilibrium microstructure have to be included in the analysis. As ϕ approaches a critical valueφ _c, the fluidity of concentrated dispersions slows down drastically. This percolation thresholdφ _c scales ad (AP)^−0.5, whereA andP are related to the repulsive interparticle potential and microstructure, respectively. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Recent Beijing Spectroscopy (BES) results

Recent experimental results from Beijing Spectroscopy (BES) are reviewed, including the hadron spectroscopy from J/ψ decays, and a number of new states are found or confirmed, including σ, κ, X(1835), ωφ threshold enhancement in J/ψ→γωφ, a broad resonance in J/ψ→K ⁺ K ⁻ π ⁰, decay studies of ψ(2S) and χ _CJ , as well as the results of ψ(3770) non-D decays. The current status of BEPCII/BESIII, the major upgrade of BEPC/BESII, is also reported. Supported by the National Natural Science Foundation of China (Grant No. 10491300)     

The nonlinear optical susceptibility and electro-optic tensor of ferroelectrics: first-principle study

The nonlinear optical properties of some ABO₃ materials (BaTiO₃, KNbO₃, LiTaO₃ and LiNbO₃) are studied by density functional theory (DFT) in the local density approximation (LDA) expressions based on first-principle calculations. Our goals are to give the details of the calculations for linear and nonlinear optical properties, including the linear electro-optic (EO) tensor for some ABO₃ structures with oxygen octahedral structures using first-principles methods. These results can then be used in the study of the physics of ferroelectrics, specifically, we present calculations of the second harmonic generation response coefficient X _ijk ⁽²⁾ (−2ω, ω, ω) over a large frequency range for ABO₃ crystals. The electronic linear EO susceptibility X _ijk ⁽²⁾ (−ω, ω,0) is also evaluated below the band gap. These results are based on a series of the LDA calculations using DFT. Results for X _ijk ⁽²⁾ (−ω, ω,0) are in agreement with experiments below the band gap. The results are compared with the theoretical calculations and the available experimental data.     

Enhanced third harmonic generation by introducing quasi-phase mismatches due to electro-optic effect

Third harmonic can be realized by the coupled second-harmonic (ω₁ + ω₁ → ω₂) and sum-frequency (ω₁ + ω₂ → ω₃) generation. However, in quasi-phase matching conditions, the efficiency of third harmonic is usually low due to the larger coupling coefficient ratio. In this paper, the third-harmonic generation in a periodically poled LiTaO₃ has been experimentally studied, where the electro-optic effect was employed to manipulate the phase mismatches and energy distribution of the coupled waves. With the DC electric field varying from 0 to 140 V/mm, the output of third harmonic can be enhanced from about 95 to 312 mW. The method provides a simple and convenient way to control the efficiencies of frequency conversion.     

Community overlays upon real-world complex networks

An approximation for the dynamic structure factor S(q, ω) of the linear harmonic chain with periodic boundary conditions is obtained from a recurrence relation approach. It is compared with (numerically) exact results for S(q, ω). Explicit expressions for the moments of the structure factor are obtained from the short time expansion up to order n = 12. For the long-wavelength as well as the deep-inelastic limit, simple expressions are derived permitting to some extent analytic results for S(q, ω). Introducing a linear regression, an approximation scheme is defined which shows excellent agreement with the numerical results.     

The BES f<Subscript>0</Subscript>(1810): a new glueball candidate

We analyze the f₀(1810) state recently observed by the BES collaboration via radiative J/ψ decay to a resonant φω spectrum and confront it with DM2 data and glueball theory. The DM2 group only measured ωω decays and reported a pseudoscalar but no scalar resonance in this mass region. A rescattering mechanism from the open flavored KK̄ decay channel is considered to explain why the resonance is only seen in the flavor asymmetric ωφ branch along with a discussion of positive C-parity charmonia decays to strengthen the case for preferred open flavor glueball decays. We also calculate the total decay width of a glueball with this mass to be roughly 100 MeV, in agreement with the narrow, newly found f₀, and smaller than the expected estimate of 200–400 MeV. We conclude that this discovered scalar hadron deserves further experimental investigation, especially in the KK̄ channel, and if shown to be different from the f₀(1710), will become a solid glueball candidate. Finally we comment on other, but less likely, possible assignments for this state.     

Measurement of light mesons at RHIC by the PHENIX experiment

The PHENIX experiment at RHIC has measured a variety of light neutral mesons (π ⁰, K _S ⁰, η, ω, η ^′, φ) via multi-particle decay channels over a wide range of transverse momentum. A review of the recent results on the production rates of light mesons in p + p and their nuclear modification factors in d + Au, Cu + Cu and Au + Au collisions at different energies is presented.