2000年, 第33卷, 第3期　
刊出日期：2000-04-30

  

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  A Prediction of a New Dibaryon System (Ω^-Ω^-)_Jπ=o⁺

  ZHANG ZongYe, YU YouWen, CHING ChengRui, HO TsoHsiu, LU ZhongDao

  理论物理通讯. 2000, 33(3): 321-328.

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  The structure of a new dibaryon (ΩΩ)_o+ is studied and predicted in the framework of the chiral SU(3) quark model by solving a resonating group method equation. The binding energy of this dibaryon is around 100 MeV, the mean root square of the distance between two Ωs is 0.84 fm and the preliminary estimated mean lifetime is about two times longer than that of the free Ω. All these interesting properties and also the two negative charge units it carried could make it be easily identified experimentally in the heavy-ion collision process. The production probability of this new dibaryon in 158A GeV Pb+Pb collision is estimated using the thermal model, which is of the order of 10^-6 to 10^-5 per event; And it is expected, that with the increase of temperature, the production rate will also be increased.
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  Theory of Coexistence of Charge-Ordering and Antiferromagnetic Phases in R_0.5A_0.5Mn0₃

  SHAO JianFei, TIAN GuangShan, LIN TsungHan

  理论物理通讯. 2000, 33(3): 329-334.

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  Based on a model Hamiltonian with the nearest-neighbor Coulomb interaction of the itinerant e_g electrons, we investigated the possibility of the coexistence of the charge-ordering phase and the antiferromagnetic phase for the manganites R_i-xA_xMn0₃ with the doping of x = 0.5. Three different types of the magnetic configurations (CEtype antiferromagnetism, simple antiferromagnetism, and ferromagnetism) have been compared by numerical calculation under the mean-field approximation. We found that the charge-ordering phase may coexist with the CEtype antiferromagnetic phase if the nearest-neighbor Coulomb interaction exceeding a certain critical value.
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  Nonclassical Effects in Polariton System

  ZOU Jian, SHAO Bin, XING XiuSan

  理论物理通讯. 2000, 33(3): 335-340.

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  In this paper we study a model polariton system. With the photons and the phonons being initially prepared in coherent state and vacuum state respectively, we show that as time evolves, the distributions of photons, phonons, and polaritons can be sub-Poissonian, and the photon quadrature squeezing, the phonon quadrature squeezing, and the polariton quadrature squeezing can exist in this system.
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  Interference Behaviors of Resonant Transport Through a Mesoscopic System with ac Responses

  ZHAO HongKang

  理论物理通讯. 2000, 33(3): 341-348.

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  Time-dependent interference behaviors on currents transporting through a mesoscopic system are investigated by using the Keldysh nonequilibrium Green function technique. The system is composed of a quantum dot coupled with two electron reservoirs. The electrons in the quantum dot are perturbed by two microwave fields (MWFs) through gate. The MWFs cause the energy level splitting in the quantum dot to form multi-channel for the tunneling current, and these branches of current interfere to produce stable oscillation. The resulting oscillation of current is strongly associated with frequency relations between MWFs. The timedependent current is the consequence of resonant effects for electrons resonating with quantum dot state and with MWFs. We present numerical calculations for the cases where the Coulomb interaction U = 0. Negative temporal current and differential conductance are observed even if the dc bias is not small. We compare the results with corresponding quantities in the system perturbed by single MWF.
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  Energy Spectra of Three-Electron Quantum Dots

  XIE WenFang, CHEN ChuanYu

  理论物理通讯. 2000, 33(3): 349-354.

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  By making use of the method of few-body physics, the energy spectra of three electrons confined by two-dimensional and three-dimensional quantum dots (QDs) are investigated. Using the present results, the size and shape effects of QDs on the spectra are revealed.
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  Electronic Properties of Fullerenes for Two Kinds of Hybridized Orbits

  TONG GuoPing

  理论物理通讯. 2000, 33(3): 355-358.

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  The electronic hopping energies and the band structure of a neutral C₆₀ molecule for two kinds of hybridized orbits, sp³ and sp², are studied using the Wannier function method and tight-binding approximation model, respectively. By comparison, the sp³ hybridized type is superior in the band structure obtained by employing the Wannier function method. When the effective nuclear charge number Z = 1.148 the energy gap (t_lu-h_u), bandwidth (t_3g-a_g) and threshold value (t_3g-h_u) of the ionization energy are 1.70 eV, 11.35 eV and 7.69 eV, respectively. These results are in accord with the experimental values.
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  Initial Order Mixing in the Kinetic Ashkin-Teller Model

  LI ZhiBing, LIU XiaoWei, PAN ZhiGang, Lothar Schülke

  理论物理通讯. 2000, 33(3): 359-364.

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  We suggest the existence of initial order mixing in the short-time evolution of the kinetic Ashkin-Teller model. The phenomenological short-time scaling laws are tested with numerical simulation.
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  A Kind of Neural Network Model Displaying Self-Organized Criticality

  HUANG Jing, CHEN TianLun

  理论物理通讯. 2000, 33(3): 365-370.

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  Based on the LISSOM model and the OFC earthquake model, we introduce a selforganized neural network model, in which the distribution of the avalanche sizes (unstable neurons) shows power-law behavior. In addition, we analyze the influence of various factors of the model on the power-law behavior of the avalanche size distribution.
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  The Nondynamical r-Matrix Structure of the Elliptic Ruijsenaars-Schneider Model with N = 2

  HOU BoYu, YANG WenLi

  理论物理通讯. 2000, 33(3): 371-376.

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  We demonstrate that in a certain gauge the elliptic Ruijsenaars-Schneider model with N = 2 admits a nondynamical r-matrix structure and the corresponding classical rmatrix is the same as that of its nonrelativistic counterpart (CalogereMoser model) in the same gauge. The relation between our (classical) Lax operator and the Lax operator given by Ruijsenaars is also obtained.
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  Explicit N-Solit on Solution of the Unstable Nonlinear Schrödinger Equation

  CHEN ZhiDe, CHEN XiangJun, HUANG NianNing

  理论物理通讯. 2000, 33(3): 377-382.

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  The unstable nonlinear Schrodinger (NLS) equation is solved by the inverse scattering transform. Based on the constructed Zakharov-Shabat equation, it is shown that the soliton solution of the unstable NLS equation can be known from the soliton solution of the usual NLS equation by simply exchanging the tariables. The explicit N-soliton solution and the position shifts due to the collision are thus calculated.
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  Generalized Lie Symmetries and the Integrability of Generalized Emden-Fowler Equations

  QU ChangZheng

  理论物理通讯. 2000, 33(3): 383-388.

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  Generalized Lie symmetries and the integrability of generalized Emden-Fowler equations (GEFEs) are considered. It is shown that the constraint which the variable-coefficient functions must satisfy for the GEFEs to have infinite-dimensional symmetry algebras is precisely the same as this in order that the equation may be transformed into the integrable Emden-Fowler equation. fiom the nature of the symmetry vector fields one can write down the integrals of motion for the above systems. The structure of the symmetry algebras is also presented.
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  Average Nuclear Binding Energies in a Lee-Wick Type Model

  ZHANG QiRen, GAO ChunYuan

  理论物理通讯. 2000, 33(3): 389-396.

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  We find: (i) The Lee-Wick type relativistic mean-field theory with finite nucleon size effect can reproduce the binding energies for all nuclei over the nuclide table quite well. For 1654 nuclei, whose mass numbers range from 16 to 263 and charge numbers range from 8 to 106, the calculated binding energies are near to the corresponding experimental values with a systematical deviation of about 5.74%. (ii) The lowering of the calculated nuclear masses, by including Coulomb energy into the variational calculations, is very small.
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  ΔI = 1 Staggering in Doubly Odd Superdeformed Nuclei

  WU ChongShi, LI ZhongHua

  理论物理通讯. 2000, 33(3): 397-404.

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  The ΔI = 1 staggering in doubly odd superdeformed nuclei is systematically investigated. Large-amplitude staggerings emerge in a series of the signature partners. The behavior is analyzed and parametrised in the conventional collective model. The spins of signature partner pairs are assigned in ab and modified ab expressions.
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  Positive Parity States in Even-Even Te Isotopes

  LI ZhongZe, LIU FengYing, ZHU LingYan, LI YanSong, NIU Li

  理论物理通讯. 2000, 33(3): 405-410.

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  The positive-parity collective states in the even-even ^116~130 Te isotopes are studied in the framework of interacting boson model. A schematic Hamiltonian able to describe the transition from U(5) to SU(3) dynamical symmetry is used. It is found that the spectra can be well described by the transition from vibration to rotation. The behavior of the 0₂⁺ state can be partially described by the model, suggesting that the state is mainly composed of the normal sd configuration, but is influenced by the cross-shell excitation across the Z = 50 shell.
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  Charge Exchange Component of n-p Interactions

  CHEN XiaoLin, LU DaHai, YANG LiMing

  理论物理通讯. 2000, 33(3): 411-416.

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  An extra term of n-p effective interaction containing charge exchange component is proposed and applied to treating odd-mass nuclei with shape coexistence. The energy spectra and some E2 transition branching ratios are calculated for odd-A nuclei ^113~125Sb,^115~127I. With the inclusion of new term, an overall agreement with experiment is much improved.
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  q-Deformed U(5) Limit in s, d IBM for Nuclei

  FANG XiangZheng, GUO JianYou, LI XianYin, RUAN TuNan

  理论物理通讯. 2000, 33(3): 417-420.

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  The q-deformed Hamiltonian with U(5) symmetry in s , d interacting boson model can be constructed by using quantum algebra SU_P (2), SU_q(1,1) and q-deformed boson operator. The energy spectra and E2 transition rates of ^110~114Cd iso topes are calculated. The calculated results agree with the experimental data rather well. Analyses on the calculated results show that the q-deformed U(5) limit is deviated from the symmetry in the original model and the degree of deviation is dependent on the deformation parameter.
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  Bilinear R-Parity Violation and τ^干κ^土 Mixing Production in e⁺e^- Colliders

  CHANG ChaoHsi, FENG TaiFu, SHAN LianYou

  理论物理通讯. 2000, 33(3): 421-430.

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  An extended minimum supersymmetric standard model, characterized by bilinear R-parity violations through the third generation lepton number (τ) in superpotential and the soft breaking SUSY tefms, is constructed. The masses of CP-odd Higgs bosons and those of charged Higgs bosons are estimated with proper formulation and possible parametrization. Several interestingfeatures, such as the mixing among τ lepton and charginos etc., are discussed precisely. Taking an example, we compute the ‘mixing production’ e⁺e^- → τ^干κ_i^土(i = 1, 2) cross sections in e⁺e^- colliders, where τ^干κ_i^土 (i = 1, 2) denote the physical τ lepton and the lightest charginos respectively.
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  Contribution of Penguins to the Nonspectator Effects in B^-, B^O, Λ_b Decays and the Missing Charm Problem

  DAI WuSheng, LI XueQian, ZHAO Gang

  理论物理通讯. 2000, 33(3): 431-436.

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  Taking the nonspectator contributions from the "tree" level four-quark operators and the penguin-induced operators into account we recalculate the charm number n_c in B decays. We find that for B^- and Λ_b, penguin contribution can be neglected, while for B_d^o it is dominant if the nonfactorization factor (t^at^a)is not sizably large. Some new physics may be needed to meet the present data.
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  Corrections from PGB to the Single-Top-Quark Production at the Fermilab Tevatron in the Technicolor Models

  CAO YiGang, JIAO ZhengKuan

  理论物理通讯. 2000, 33(3): 437-444.

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  We calculate one-loop PGB (pseudo-Goldstone bosons) corrections to the cross section for the single-topquarkproduction via qq' → tb at the Fermilab Tevatron in the MWTCM (multiscale walking technicolor model) and topcolor assisted MWTCM. The corrections from PGB in the topcolor assisted MWTCM decrease the production cross section only a few percent, and the corrections from PGB in the MWTCM are found to exceed -l0%, which might be observable at a high-luminosity Tevatron.
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  Space-Like Form of Bethe-Salpeter Equation: Scatter State

  WANG An Min, RUAN Tu Nan

  理论物理通讯. 2000, 33(3): 445-450.

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  According to Dirac, and based on our space-like form of Bethe-Salpeter equation of bound state, we extend the definition of the space-like wavefunctions and derive out the spacelike form of Bethe-Salpeter equation for scatter state. The solution of the inhomogeneous term is also obtained in detail so as to clarify the significance of inhomogeneous space-like form of Bethe-Salpeter equation for scatter state. Moreover the translation method is finally discussed.
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  Real-Time Thermal Field Theory Analyses of 2D Gross-Neveu Model

  ZHOU BangRong

  理论物理通讯. 2000, 33(3): 451-456.

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  The discrete symmetry breaking and possible restoration at finite temperature T are analyzed in 20 Gross-Neveu model by the real-time thermal field theory in the fermion bubble approximation. The dynamical fermion mass m is proven to, be scale-independent and this fact indicates the equivalence between the fermion bubble diagram approximation and the meanfield approximation used in the auxiliary scalar field approach. Reproducing of the nonzero critical temperature T_c = 0.567m(O), m(0) is the dynamical fermion mass at T = 0, shows the equivalence between the real-time and the imaginary-time thermal. field theories in this problem. However, in the real-time formalism, more results including absence of scalar bound state, the equation of criticality curve of chemical potential-temperature and the ln(T_c/T) behavior of m² at T ≤ T_c can be easily obtained. The last one indicates the second-order phase transition feature of the symmetry restoration.
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  Symmetry Breaking in Finite Volume-a Study in the O(N) Model

  LIU Chuan

  理论物理通讯. 2000, 33(3): 457-462.

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  Spontaneous symmetry breaking plays a crucial role in quantum field theories and it occurs only for systems with infinite degrees of freedom. For a system in a large but finite volume, although the symmetry is not broken spontaneously, an adiabatic approximation can be applied to study the would-be broken symmetry. Lattice O(N) model is studied within the Hamiltonian approach. It is shown that the low-lying spectrum of the system can be explained using an adiabatic, or Born-Oppenheimer approximation, which turns out to become 1 an expansion in the inverse power of volume. In the infinite volume limit, the symmetry is broken while in the finite volume the slow rotation of the zero-momentum mode restores the symmetry and gives rise to the rotator spectrum, which has been observed in real Monte Carlo simulations.
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  A Hamiltonian Perturbative Study of Lattice 0 (N) Model in the Broken Phase

  LIU Chuan

  理论物理通讯. 2000, 33(3): 463-468.

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  The lattice O(N) model, defined on a large but finite three-dimensional cubic lattice, is studied using the Hamiltonian approach in bare perturbation theory in the broken phase. Renormalization is carried out to O(λ_o) and the results are compared with those obtained using the conventional Lagrangian approach in the infinite volume limit. Complete agreement is found between the two methods.
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  2D H-Atom in an Arbitrary Magnetic Field via Pseudoperturbation Expansions Through the Quantum Number l

  Omar Mustafa, Maen Odeh

  理论物理通讯. 2000, 33(3): 469-476.

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  The pseudoperturbative shifted-1 expansion technique is introduced to determine nodeless states of the 2D Schrodinger equation with arbitrary cylindrically symmetric potentials. Exact energy eigenvalues and eigenfunctions for the 2D Coulomb and harmonic oscillator potentials are reproduced. Moreover, exact energy eigenvalues, compared with those obtained by numerical solution (V.M. Villalba and R. Pino, J. Phys.: Condens. Matter 8 (1996) 80671, were obtained for the hybrid of the 20 Coulomli and oscillator potentials.
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  Geometric Phase and Bose-Einstein Condensate

  WANG ZhengChuan, LI BoZang

  理论物理通讯. 2000, 33(3): 477-480.

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  We show that a geometric phase may appear in the Bose-Einstein condensate (BEC) in which an adiabatic procedure happens, then a perturbation expression of geometric phase is obtained for the case of time-averaged orbiting potential trap. The phase caused by the adiabatic bias magnetic field in one BEC may interfere with another, which is similar to the phase interference of Aharonov-Susskind effect, and can be observed by experiments.
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  Optical Solitons with Gaussian Tails

  HUANG GuoXiang, HU BamBi

  理论物理通讯. 2000, 33(3): 481-486.

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  Based on an extended method of multiple scales, an analytical description of the optical solitons in a model for the propagation of nonlinear pulses in dispersion-managed optical fibers is presented. The results show that the optical pulses can be expressed by quantummechanical wavefunctions of a linear oscillator, which have tails of Gaussian type, modulated by hyperbolic secant solitons of the nonlinear Schrödinger equation.
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  Angular Momentum and Energy Structure of the Coherent State of a 2D Isotropic Harmonic Oscillator

  LIU YuFeng, HUO WuJun, ZENG JinYan

  理论物理通讯. 2000, 33(3): 487-490.

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  The angular momentum structure and energy structure of the coherent state of a 20 isotropic harmonic oscillator were investigated. Calculations showed that the average values of angular momentum and energy (except the zero-point energy) of this nonspreading 20 wavepacket are identical to those of the corresponding classical oscillator moving along a circular or an elliptic orbit.
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  Superconductivity in Bilayer Cuprates

  YIN WeiGuo, HUANG MingSheng

  理论物理通讯. 2000, 33(3): 491-494.

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  We calculate the stability of d_x²-y² wave superconducting state in bilayer cuprates within the antiferromagnetic and van Hove scenario. We find an increment ~10 K of T_c^max with the growth from one plane to a bilayer when the hole pairing induced by the spin-wave exchange is included.
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  Applicationo f the Mellin Transformation in Proving the Completeness Relation. of the Charged Coherent State

  FAN HongYi, ZOU Hui

  理论物理通讯. 2000, 33(3): 495-498.

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  We show that the completeness relation of the charged coherent state can be obtained by using the Mellin transformation and contour integration method. As a result, a modification of the completeness relation of the charged coherent state given by D. Bhaumik et al. (J. Phys. A: Math. Gen. 9 (1976) 1507) is presented.
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  Folding Cluster Model for 6Li Scattering from ⁹Be and ¹⁶O

  A. A. Farra

  理论物理通讯. 2000, 33(3): 499-502.

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  The elastic scattering of ⁶Li from ⁹Be and ¹⁶0 has been analyzed in terms of a phenomenological and microscopic potential. The real potential was generated from either a double-folding calculation or a single-folding model. A Woods-Saxon form was used for the imaginary potential. The double-folding analysis provides reasonably good fits to the experimental data and leads to a better description of the enhanced large angle cross sections than the phenomenological calculations.
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  Description of the Superdeformed Bands of the Lutetium Isotopes

  WANG JiaJun, ZHANG YinJing

  理论物理通讯. 2000, 33(3): 503-506.

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  In the cases with and without a perturbation possessing the S0_sdg(5) (or SU_sdg(5)) symmetry in the supersymmetry scheme with many-body interactions, superdeformed bands in the odd-A Lu isotopes ^163,165,167Lu are investigated. Quantitatively good results of γ-ray energies and dynamical moments of inertia are obtained in both of the two cases. It shows that the supersymmetry scheme with many-body interactions has almost the same power to describe the triaxial superdeformed bands as to the other superdeformed bands.
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  Generation of Superpositions of Atomic Coherent States Through Raman Atom-Field Interaction

  ZHENG ShiBiao

  理论物理通讯. 2000, 33(3): 507-509.

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  We propose a scheme for the generation of superpositions of collective atomic coherent states. In the scheme a collection of degenerate A-type three-level atoms is confined in a high-Q cavity and interacts with the cavity field in a Raman manner. Then a state reduction on the field collapses the atomic system onto a superposition state.
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  Realization of Strong Squeezing for a Macroscopic Oscillator

  ZHENG ShiBiao

  理论物理通讯. 2000, 33(3): 510-512.

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  We propose a scheme to realize strong squeezing for the motion of a cavity mirror through atom-field and field-mirror interactions. We also show how to generate superpositions of several coherent states along a line for such a macroscopic oscillator.