1991年, 第16卷, 第2期　
刊出日期：1991-09-15

  

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  Theory of a Heavy Particle Coupled with an Electron Gas

  Mingli ZHOU, Yurnei ZHANG, Xiang WU

  理论物理通讯. 1991, 16(2): 129-138.

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  We study a heavy particle moving in metallic environment Which is represented by a bath of degenerate electron gas. Assuming that the Ferrni energy of the screening clcctrons is a large scale in comparison with tlrat of heavy particle, we calculate the partition furlction of the whole system by using functional integral techniques with Grassman variables. After integrating out the freedom of electron gas, it can be found that the hopping of the particle is suppressed by the bath. The effective action is treated self-consistently. We find that in the strong coupling limit the phase shift of the electron on the local Fermi surface tends to π/N , leading to the instability of Fermi sea and tlre formation of resonant state. A "Kondo" temperature is introduced to define the width of resonant state and to clraracterize the boundary from quantum to classical dyriamics of the particle as well.
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  A Theory on the Mixture of Fermi-Liquid and Spin-Liquid

  Shijie XIONG

  理论物理通讯. 1991, 16(2): 139-148.

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  The delocalization of the doped holes in a CuO₂ sheet of the superconducting oxides is investigated. It leads to the formation of a mixture of Fermi-liquid and spin-liquid. The exchange interaction between them is proven to be weak and the Fermi-liquid feature of the itinerant holes is ensured. This exchange leads to the long-range RKKY interaction among the isolated spins embedded in the spin-liquid, and under certain condition can produce an incommensurate spin configuration. For the Fermi-liquid, the spin-flip part of this exchange provides a pairing mechanism of the singlet type in high frequency window. It is found that the Coulomb repulsion within a pair is suppressed by the pseudopotential effect in the unscreened case. The relation to other mechanisms which also produce the pairing in high frequency window is discussed. The possibility of co-appearance of superconductivity and incommensurate spin configuration is analyzed. Several critical doping concentrations are estimated.
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  Stochastic Resonance in Different Potential systems

  Gang HU, Dechun GONG, Guangrong QIN, Xiaodong WENG, Chunyuan YANG

  理论物理通讯. 1991, 16(2): 149-154.

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  In the study ofstochastic resonance, the bistable potential -ax²/2+bx⁴/4 has been extensively used. In the present paper general potential systems are considered. It is found that the signal-to-noise ratio in the output can be more effectively enhanced if we choose prober Potential forms.
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  The Effect of Correlation on the Localization Properties of Antiferrornagnets

  Jie YANG, Juelian SHEN, Fuclio PU

  理论物理通讯. 1991, 16(2): 155-160.

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  The random uniaxial anisotropy Heisenberg antiferromagnetic model is studied within the framework of weak localization theory. It is found that the correlation effect strongly changes the form of the phase diagram of Anderson transition, and the coupling of the random scattering with the spin-waves interaction gives rise to an energy shift in spin wave spectrum, it is also sensitive to tlre correlation.
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  Variational Cumulant Expansion for Spin Systems on a Triangular Lattice

  Jinmin YANG

  理论物理通讯. 1991, 16(2): 161-166.

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  The variational cumulant expansion is extended to two-dimensional Potts spin models with two-body interactions defined on a triangular lattice. As a test, the Z(3),Z(4) and Z(5) Potts models are treated. The phase transition points given by this approach are in good agreement with the exact values.
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  Numerical Solution of the spin-1/2 Heisenberg Antiferromagnetic Chains Using a Projector Method

  Gang SUN

  理论物理通讯. 1991, 16(2): 167-172.

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  An efficient projector method is proposed to calculate the energy gap between the ground,state and the first excited state of the spin-1/2 Heisenberg antiferromagnetic chains. We exactly computed the two lowest-lying energies for the magnetization S_t^z= 0 and the lowestlying energy for S_t^z=±1 on chains up to 16 spins. The lowest-lying energy stat6 for S_t^z= 0 is a singlet ground state. The second lowest-lying energy state for S_t^z= 0 and the lowestlying energy states for S_t^z=±1 are triplet degenerate, which are the first excited energy states. We also imposed the Monte Carlo technique to estimate the lowest-lying energies for both S_t^z= 0 and 1 on longer chains up to 32 spins. We found that the singlet-triplet energy gap trends to zero as N→∞.
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  New R(x)-Matrix, L(x)-Operator and Quantum Algebra in Spin Model

  Molin GE, Xufeng LIU, Kang XUE

  理论物理通讯. 1991, 16(2): 173-178.

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  New solution of Yang-Bax ter equation for spin-1 ⊗ spin-1/2 tensorial space is derived based on the direct calculation and extended Yang-Baxterization prescription. It contains the standard solution as a special case. By employing Faddeev-Reslretiklrin-Takhtajan approach we give the correspondent quan turn algebraic structure. Tllc Yang-Daxtcrizalion.of the L-operator is also made explicitly.
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  Solutions to the Yang-Baxter Equation for the Spinor Representations of q-D_e

  Boyuan HOU, Zhongqi RIA

  理论物理通讯. 1991, 16(2): 179-194.

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  In this paper, both trigonometric and rational solutions to tlre Yang-Baxter equation associated with the spinor representations of the quantum D_l univcrsal enveloping algebras are obtained. The quantum Clebsch-Gordan matrices, the quantum projectors and the solutions are the block matrices with the dimensions of tire submatrices to Le 1 and 2^n-3, 1l', where _l' = _l/2 + 1, if _l' is even, _l' = (_l + 1)/2, if _l is odd. Tlre csplicit forms of the submatrices with the same dimensions are indcpendcrlt of _l. As esamples, we discuss the solutions for the spinor representations of the quantum D₄ to D₇, and prcscnt tlre explicit forms of those submatrices with the dimensions 1, 2, 8 and 32. Tlre corresponding representations of the braid group and the link polynomials are also computed tlrrougll a standard method.
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  Noise and Nonlinearities in (1+1)-Dimensional System

  A. F. Lawrence, G. G. LIAO, A. T. Abawi

  理论物理通讯. 1991, 16(2): 195-200.

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  We show that the Fokker-Planck equation can be applicd to noisy sine-Gordon systems,either through reduction to soliton paranlctcr or by the techniques of functional analysis.We also suggest approaches to introducing noise in the auxiliary Faddcev-Takhtadzhyan scattering equations.
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  Parametrization of Ordering Ambiguity and Its Representation in Path Integral Formalism

  Dehai BAO, Zhongyuan ZHU

  理论物理通讯. 1991, 16(2): 201-208.

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  ln this paper, we establish three different types (type I, type Ⅱ and type Ⅲ) of pararnctrization of ordering ambiguity in operator formalism of quantum mechanics and discuss their nontrivial relations. Some commonly occurred bewildcrment about ordcring problem is made clear. We also show that the ordering ambiguity exists in path intergral formalism and the representation of the ordering ambiguity in the path integral formalism (discrete schemes ) has a one-to-one correspondence with type Ⅱ parametrization of the ordering ambiguity in the operator formalism. As a result, we show that to select a physically a misled atempt，Instead, we have to work with type Ⅲ parametrization in the operator forrnalisim to reduce the ordering ambiguity by physical requirements.
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  Solution of the Puzzles in D→K(K*)_e+ve and Tansition Form Factors Among Heavy to Light and Heavy to Heavy to Mesons

  Y. L. WU

  理论物理通讯. 1991, 16(2): 209-214.

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  We present a model-independent and systematic method for calculating the matrix elements among heavy to light and heavy to heavy hadrons. The new method allows us to obtain absolutely normalized form factors at the maximum momentum transfer for Q→Q' or q' induced weak transitions among meson states such as 0^-+→0^-+,1^--),0⁺⁺,1⁺⁺ etc. It is applied to the B-meson and D-meson systems and found that the puzzles in the D→K(K')_e+ve decays can be solved nicely.
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  kiow.to Search for 'p₁ State of CC at BEPC-The Electromagnetic Transition Ψ' -+Ψ('p₁) + 2Y₁

  Chengrui CHING, Tsohsiu ⅡO, Zhijian TAO

  理论物理通讯. 1991, 16(2): 215-222.

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  Decay rate of the process Ψ'→Ψ(¹P₁)+2γ is calculated with all possible intermediate states included in the context of potential model. Out calculation shows that the branching ratio for this channel is about 10^-5.For a total production of 2×10Ψ' particles, it is possible to find out Ψ' (¹P₁) at BEPC through searching for 3γ signals.
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  Towards a Quantum Bag Dynamics (Ⅲ)-Collective Motion of the Bag

  Qiren ZHANG

  理论物理通讯. 1991, 16(2): 223-232.

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  It is showed, that under the adiabatic assumption, the quark-gluon state and the energy of a dynamic bag may be expressed as functions of its collective coordinates and their first time derivatives. The effective-lagrangian and IIamiltonian for the collective motion arethen proposed. The classical equation of coJJective motion is suggested to be used as the self-consistent equation for the force function f(R, R). The bag dynanlics is once again quantized. A set of ellipsoids and their finite combinations is recommended as a complete set of bag shapes because of its Lorentz invariance. The wave function for tlle internal motion of a hadron is therefore a function of the bag shape configuration..It may be used to average intrinsic observables and matrix elements of a hadron over the shape configuration. The zero momentum eigenstate of a hadron is constructed by making use of its translational symmetry. Finite momentum eigenstates are then constructed by Lorentz boosts. Multi-hadron states and hadron interactions are also considered.
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  Binding Energies of the Electron in GaAs-Ga_l-xAl_xAs Quantum Well Under Perpendicular Magnetic Field

  Zhongjun SHEN, Shu-an ZHANG, Shiwei GU

  理论物理通讯. 1991, 16(2): 233-236.

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  We have calculated the binding energies of the ground state of hydrogenic donor in GaAs-Ga_1-xAl_xAs quantum well of finite barrier height in the prcscnce of a magnetic field, which is taken to be parallel to the axis of growth of the quantum-well structure. We have used the strong-perturbation theory and the perturbative-variational approach. Our results are given as a function of the size of the quantum well.
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  Interchain Coupling in Polydiacelene

  Jingcui PENG

  理论物理通讯. 1991, 16(2): 237-240.

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  Interchain coupling in polydiacetylene is investigated by considering two parallel chains and taking into account a hopping of π electrorls from one chain to the other. The correction in energy and the change of polaronic bioding energy resulting from interchain coupling are calculated by using Green's function, and the results are compared with experimental data.
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  Remarks on the q-Deformation of Fermionic Oscillators

  Xingchang SONG

  理论物理通讯. 1991, 16(2): 241-244.

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  The properties of the q-deformed fermionic oscillator opcrators arc esarnir~cd. The difference between the deformed oscillators and the ordinary ones is closely related to the mullivalueness of the deformation parameter η= ln q.
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  An SU(1,1) Boson Realization Involved in Solving the Three Coupled Harmonic Oscillators' Problem

  Hongyi FAN

  理论物理通讯. 1991, 16(2): 245-248.

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  We find that a three-mode boson realization of the SU(1,1) Lie algebra is involved in solving the three coupled harmonic oscillators' problem. Tire unitary operator U, which is found to be able to transform the Fock space of a three-dimcrrsional isotropic Irarmonic oscillator into the space in which the Hamiltonian of three coupled oscillators is diagonized, is further decomposed as a quantum-mechanical rotation in three-mode Hilbert space followed by an SU(1,1) squeezing transformation. The coordinate representation of this SU(1,1) unitary operator is obtained.
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  q-Oscillators and Quantum Lie superalgebras

  Li LIAO, Xingchang SONG

  理论物理通讯. 1991, 16(2): 249-256.

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  With the help of the q-delormed bosonic and fermionic oscillation opcrators, which can be constructed from the ordinary ones, the quantum enveloping algebras of basic Lie super-algebras (BLS) B(m, n), B(0, n), C(1+n)and D(m,n)iu Ihcir Boson-Fermion oscillator representation are written down explicitly.