1997年, 第28卷, 第1期　
刊出日期：1997-07-30

  

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  Quantum Affine Superalgebra U_q(gl(1|1)) and Its

  CAI Jinfang, WANG Shikun, WU Ke, ZHAO Weizhong

  理论物理通讯. 1997, 28(1): 1-2.

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  Drinfeld's realization of quantum affine superalgebra U_q(gl(1|1)) is given based on the super version of RS construction method and Gauss decomposition.
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  Momentum Transfer and Effect of Motion of Atomic Mass Centre on an Atom-Cavity System

  YI xuexi, SUN Changpu

  理论物理通讯. 1997, 28(1): 3-8.

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  For a special ∧-type atom with dark state, the problem of momentum transfer is discussed in detail. Effect of moving mass centre on atomic dynamics for various initial conditions is also studied. The numerical results show that the Doppler effect exercised by the motion of atomic mass centre can lead to the modified phenomenon of oscillation collapse and revival in the transition probability and the atomic population inversion.
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  Effect of LO-Phonons on the Hydrogenic Impurities in a Spherical Quantum Dot

  CHEN Chuanyu, LI Waisang, JIN Peiwan

  理论物理通讯. 1997, 28(1): 9-16.

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  By applying the method of variational wavefunction and adopting the approximation of 3D-Frohlich Hamiltonian for electron-LO phonon interaction in a spherical quantum dot (SQD), we have calculated the ground-state energy E, and binding energy E_g of a bound polaron confined in a GaAs/Ga_χAl_1-χSQD. These energies vary as the value of the boundary potential of the SQD and the deviation of the position of the hydrogenic impurity from the centre of the sphere. In this system of concern, R = 2a^*, a^* is the effective Bohr radius, is an appropriate criterion for the radius R of an SQD when the effect of quantum confinement has to be considered.
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  Study of Some Factors Affecting Thermodynamic Properties of the Insulating Phase of the Periodic Anderson Lattice Model

  HU Liangbin, JIANG Huaming, YANG Fumin, SUN Jinzuo

  理论物理通讯. 1997, 28(1): 17-22.

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  Within the framework of slave-boson mean-field theory, we study the thermodynamic properties of the periodic Anderson lattice model with half-filled conduction band and one 4f electron at each primitive cell and the degeneracy N_d = 2. It is found that after taking into account the direct nearest-neighbor f-f hopping, such a periodic Anderson lattice model can exhibit both an insulating ground state and a heavy-fermion metal ground state depending on the value of the bare f energy level E_f, the hybridization matrix element V, and the direct f-f hopping strength δ. This is unlike the case neglecting the direct f-f hopping, in which such a periodic Anderson lattice model will predict an insulating ground state only.
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  SO(4) Symmetry and Off-Diagonal Long-Range Order in the Hubbard Bilayer

  SHI YU

  理论物理通讯. 1997, 28(1): 23-28.

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  Yang's η pairing operator is generalized to explore off-diagonal long-range order in the Hubbard bilayer with an arbitrary chemical potential. With this operator and a constraint condition on annihilation and creation operators, we construct explicitly eigenstates which possess simultaneously three kinds of off-diagonal long-range order, i.e., the intralayer one and the interlayer one for on-site pairing, and that for interlayer nearest-neighbor pairing. As in the simple Hubbard model there is also an SO(4) symmetry, with the generators properly defined. A sufficient condition leads to at least one of the above three kinds of off-diagonal long-range order. A constraint relation among different kinds of off-diagonal long-range order is also given. There exists a triplet of collective modes if the U(1) symmetry of a subgroup is spontaneously broken.
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  Competition Between the SDW and CDW in Quasi-One-Dimensional Organic Polymer Ferromagnet

  FANG Zhong, LIU Zuli, YAO Kailun, HU Huifang

  理论物理通讯. 1997, 28(1): 29-34.

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  The next-nearest-neighbor hopping interactions of ρ-electrons in quasi-onedimensional organic polymer ferromagnet are considered by Peierls-Hubbard model, and a set of self-consistent equations are established to optimize the system. The competition between the SDW and CDW states, which is determined by the interplay between the electron-electron correlation and the next-nearest-neighbor hopping interaction, is studied. At the CDW state,the SDW along the main chain will be tuned by the CDW. Consequently the ferromagnetic state, in which all the spins of the unpaired electrons at side freeradicals are arranged parallelly,will be no longer a stable ground state of the system.
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  The Critical Temperature of Quantum Spin Model Determined with Variational-Cumulant Expansion

  CHEN Tianlun, WANG Qing, LIU Ruijie

  理论物理通讯. 1997, 28(1): 35-40.

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  The variational-cumulant expansion (VCE)methodis used to calculate the quantum XY model, for which the trial action S₀ does not commute with the action S, with arbitrary magnitude of spin on various one-, twe and three-dimensional lattices. The free energy of the model is expanded to the third order and the analytical formulae of critical temperature T_c are given for each order. To testify this method in a wider range, the Heisenberg model on different lattices is also calculated, which has more comparable results. Weighted fitting method of statistical mathematics is adopted to predict T_c of infinite order.
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  Higher-Dimensional Integrable Models with a Common Recursion Operator

  LOU Senyue

  理论物理通讯. 1997, 28(1): 41-50.

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  Starting from any one of hereditary symmetries, we can construct a type of integrable models with arbitrary dimensions. The models with different dimensions obtained from a same hereditary symmetry possess a common recursion operator. The symmetry structures of the models are studied in their potential forms. Using the formal series symmetry approach, we can get various sets of formal series symmetries with some arbitrary functions. Generally, these sets of series symmetries are not truncated for arbitrary functions. The series symmetries wiU all be truncated if the arbitrary functions are fixed as polynomials. Some sets of nontruncated symmetries constitute generalized Virasoro algebras. The more details about the symmetries and algebras are discussed for a concrete (3+1)-dimensional KdV equation.
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  Two Theorems on the Hubbard-Hirsch Model

  WANG Zhijun, QIU Xiaoming

  理论物理通讯. 1997, 28(1): 51-56.

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  In this paper, the two theorems on the Hubbard-Hirsch model are shown rigorously. For positive on-site interaction U, the model on some bipartite lattices has a weak ferromagnetic ground state at half filling. For negative U, the ground state of the model on some bipartite lattices possesses off-diagonal long-range order within a finite range of the electron filling factor.
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  Clebsch-Gordan Coefficients for Two-Parameter Deformed Quantum Algebra SU(1,1)_q,s(Ⅱ)

  YU Ge, ZHANG Dexing, YU Zhaoxian

  理论物理通讯. 1997, 28(1): 57-62.

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  Abstract The Bargmann represen tations in the tensor product space of the irreducible representations for the two-parameter deformed quantum algebra SU(1,1)_q,s corresponding to the negative discrete series (b) are introduced, and the corresponding Bargmann expressions for the bases of irreps, the coherent state and the operators are also derived. The Clebsch-Gordan coeficients (CGC) for the two-parameter deformed quantum algebra SU(1,1)_q,s corresponding to the negative discrete series (b) are obtained.
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  EM Transition Sum Rules Within the Framework of sdg Proton-Neutron Interacting Boson Model, Nuclear Pair Shell Model and Fermion Dynamical Symmetry Model

  ZHAO Yumin

  理论物理通讯. 1997, 28(1): 63-70.

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  By the techniques of the Wick theorem for coupled clusters, the no-energy-weighted electromagnetic sum-rule calculations are presented in the sdg neutron-proton interacting boson model, the nuclear pair shell model and the fermion-dynamical symmetry model.
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  The Pion-Recoil Current and Quark-Cluster Effects of Electromagnetic Form Factors of Deuteron

  CHENG Tansheng, ZHONG Yushu, LU Lanchun

  理论物理通讯. 1997, 28(1): 71-78.

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  The electromagnetic form factors of deuteron are investigated on hybrid quarkhadron model, whexe meson exchange and six-quark clusters are taken into account. It is found that pion-recoil current and six-quark clusters have important effects on charge form factor, magnetic structure function and tensor polarization, which are all sensitive to the interaction between nucleons. The theoretical predictions agree well with new experimental data.
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  Four-Generation Condensate Scheme Without the Fourth Generation of Leptons

  ZHOU Bangrong

  理论物理通讯. 1997, 28(1): 79-84.

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  The renormalization group (RG) analyses show that in the four-generation fermion condensate scheme of electroweak symmetry breaking without the extra fourth generation of leptons thelimitation to the compositeness scale Λ could be greatly loosened and up to Λ<10¹⁰ GeV if the masses of the extra fourth generation of quarks are demanded to be bigger than the topquark mass m_t = 180 GeV. However, the mass constraints 2(m_Q)_minh⁰<2(m_Q)_max between the Higgs boson h⁰ and its constituent Q-fermions are no longer totally valid for Λ>10⁵ GeV. The ~redicted masses of the fourth generation of quarks and the Higgs boson will be larger than the corresponding ones in the four-generation quark-lepton scheme. The stability of the results for variation of the compositeness boundary conditions could be explained more clearly.
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  Study of Baryon Antibaryon Rapidity Correlation in e⁺e^- Annihilation by Quark Combination Model

  SI Zongguo, XIE Qubing, WANG Qun

  理论物理通讯. 1997, 28(1): 85-94.

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  We use quark combination model to study baryon antibaryon rapidity correlation in e⁺e^- annihilation and compare our predictions with the available data. We find that these results and relevant properties are all consistent with data. So the evidence to rule out quark combination model which has long been cited in literatures does not exist.
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  Weak Decays of D and D_s Mesons in a Relativistic Quark Model

  LIU Jiafu, CHAO Kuangta

  理论物理通讯. 1997, 28(1): 95-100.

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  The transitions of D and D_s, mesons to light vector states are studied in a relativistic constituent quark model based on the Bethe-Salpeter formalism. The form factors are calculated, and the branching fractions for both semileptonic and nonleptonic decays are given. The results show that the form factors for these transitions deviate substantie from the request of heavy quark symmetry. All the branching ratios for D and D_s semileptonic decays are found to be consistent with data, whereas the calculations of nonleptonic D and D_s decays under the factorization assumption do not agree with experiments. This confirms the conjecture that the factorization scheme is much less applicable in D and D_s decays than in B and B_s decays.
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  Proton Decay and Deficit Angle of Cosmic String

  LI Xinzhou

  理论物理通讯. 1997, 28(1): 101-106.

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  A cosmic string may catalyze baryon number violating processes with strong interaction cross sections rather than the much smaller geometric cross sections. The catalysis cross sections are calculated using the second-quantized prescription. Our results show that catalysis cross sections depend sensitively on the deficit angle of cosmic string.
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  Interaction of Soliton with the Boundary in the Parametrically Excited Water Trough

  WANG Wei, WANG Xinlong, WANG Junyi, WEI Rongjue

  理论物理通讯. 1997, 28(1): 107-110.

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  The interaction of solitary wave with the boundary of the parametrically excited water trough is studied, numerically. Four cases of the interaction found experimentally are verified by the numerical simulation using the Miles' equation. The physical origin of the interaction is also discussed, and a force between the soliton and the boundary is obtained.
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  The Neoclassical Fluxes and Bootstrap Current of the Energetic Alphas in the Presence of the Electric Field

  QI Changwei, DING Houchang

  理论物理通讯. 1997, 28(1): 111-116.

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  The neoclassical transport theory of the energetic alpha particles in Tokamak is developed by means of a variational principle. The neoclassical particle, energy and current fluxes of the energetic alphas are evaluated in the presence of the electric field and in the case of retention both of electron and ion drag and pitch angle scattering by the background ions. The alpha bootstrap current and Ware flux are respectively δ^-1 (δ is the inverse aspect ratio)times larger than and opposite in direction to those obtained in the past.
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  Tunneling Effect of Atom Through Cavity Fields

  WANG xiaoguang, QI Tingzhu

  理论物理通讯. 1997, 28(1): 117-120.

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  Based on the model proposed by B.G. Englert et al., westudy the tunneling effect of an atom through one or two cavities while the atom is slow enough. This is purely the quantum, effect of atom. When an atom is in excited state and cavity fields in single number state, the atom will experience a potential well and a potential barrier. The. transmission probability is obtained as the contributions of two parts, one is the transmission probability through the potential well and another the tunneling probability through the potential barrier.
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  Symmetry Breaking in the Jaynes-Cummings Model Without RWA

  XIE Ruihua, XU Gong'ou

  理论物理通讯. 1997, 28(1): 121-124.

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  The relationship between the field and atomic squeezing has been studied in the Jaynes-Cummings model without the rotating- wave approximation (RWA). For weaker coupling(<10^-2), the symmetry between the field and atomicsqueezing (SFAS) has been exposed. When the coupling strength is up to the magnitude of order 10^-2, the SFAS begins to be destroyed. For sufficientlys tronger coupling(≈1), the squeezing disappears almost entirely and the SFAS is destroyed thoroughly.
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  An Analysis of Pion-¹³C Elastic Scattering and Single Charge Exchange Reaction

  REN Yongjian, MA0 Guangjun, LIU Xiaoyun, ZHAO Enguang

  理论物理通讯. 1997, 28(1): 125-128.

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  The π⁺-¹³C elastic scattering at 162 MeV and ¹³C(π⁺,π⁰)¹³N at 165 MeV are analyzed in a model in which the nuclear state is assumed to consist of a valence nucleon and a ¹²C core described by a three a-duster wavefunction and the cross section is calculated in the Glauber theory. A good agreement between theory and experiment is obtained and the results also indicate the important influence of the core on the processes.