1997年, 第27卷, 第1期　
刊出日期：1997-01-30

  

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  Improving KFR Theory by Dressing Atomic Initial States

  De-Hai BAO, Shi-Gang CHEN

  理论物理通讯. 1997, 27(1): 1-8.

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  This paper is devoted to nonperturbative theoretical treatments for the above-thresholdionization (ATI) phenomena. It is shown that the bare atomic initial state approximation in Keldysh-Faisal-Reiss (KFR) theory leads to a fundamental theoretical difficulty and thus, has to be modified by properly dressing the atomic initial state with an. appropriate laser-electron interaction term. The analytical result of the improved S-matrix for general situations is obtained and is applied to hydrogen Is-state with linearly polarized laser of various intensities. The numerical simulations of our applications indicate that the improved theory is not only more reasonable on theoretical aspect, but also closer to experimental measurements.
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  Theoretical Calculations of Rydberg Stark Effect of Hydrogen Atom

  Jian-Guo RAO, Bai-Wen LI

  理论物理通讯. 1997, 27(1): 9-14.

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  The Stark shifts and widths of the highly excited states near the classical ionization threshold of a hydrogen atom are calculated by the B spline technique plus complex scaling method. The Lanczos method has been used in our calculations and is proved to be powerful. Our results are in agreement with the experimental results and theoretical ones obtained by other methods. The method can also be used to calculate the same problem for atoms in parallel and cross electric and magnetic fields.
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  Quantum Light Excitation of Atoms in Ideal Bose-Einstein condensate

  C. P. SUN, S. R. ZHAO

  理论物理通讯. 1997, 27(1): 15-20.

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  The spectrum shape of atomic radiation in the case of ideal Bose-Einstein condensate (BEC)excited by quantized light is derived through the Wigner-Weisskopf approximation. Besides the split and gap in the excitation spectrum, a doublet structure appears in the emission spectrum with different widths for the non-resonant case and the same widths for the resonant case. The survival probability is found to decrease exponentially for the non-resonan t case and with oscillation for the resonant case. A suppressed radiation also appears in the nonresonant case. All these results can be used to detect the existence of BE condensation.
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  Quantum XY Spin-Glass Model with Ferromagnetic Couplings and Plane Dzyaloshinski-Moriya interactions

  Yu-Min SHANG, Lin YI, Kai-Lun YAO

  理论物理通讯. 1997, 27(1): 21-26.

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  In the generalized quantum replica symmetric approximation, a quantum XY spin-glass model with ferromagnetic coupling and planar Dzyaloshinski-Mariya (DM) interactions is investigated theoretically. Entropy and specific heat are calculated numerically as well as spin self-interactions and spin-glass order parameters for spin S = 1. It is found that the doublecusp of the specific heat, which corresponds to the collinear ferromagnetic and the paramagnetic ferromagnetic transitions respectively, .coincides completely due to DM-anisotropy interactions. Additionally, the local susceptibility and the spontaneous magnetization are evaluated numerically.
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  Percolating Theory on the Magnetic Transition in the Hubbard Model

  C. C. WAN

  理论物理通讯. 1997, 27(1): 27-32.

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  We show that the understanding of the magnetic transition of the Hubbard model can be made easier by decomposing the ground-state wavefunction into different components, which represent the ground state of different spin clusters.
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  Spin-Wave Theory of Frustrated 1D Spin-1/2 Ant iferrornagnetic Chain

  Hai-Yan ZHANG

  理论物理通讯. 1997, 27(1): 33-36.

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  The spin-wave theory is used to study the ID spin-1/2 antiferromagnetic chain. The elementary excitations are found by equations of motion with decoupling approximation. As required, the energies are triply degenerate.
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  Suppressing Chaos and Transient in Parameter Perturbed Systems

  H. P. FANG, G. W. HE, L. Y. CAO

  理论物理通讯. 1997, 27(1): 37-40.

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  The systems with some system parameters perturbed are investigated. These systems might exist in nature or be obtained by perturbation or truncation theory. Chaos might be suppressed or induced. Some of these dynamical systems exhibit extraordinary long transients, which makes the temporal structure seem sensitively dependent on initial conditions in finite observation time interval.
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  Behavior of the Hamiltonian's Eigenstates Around the Avoided Level Crossing

  Quan-Lin JIE, Gong-Ou XU, Wen-Ge WANG

  理论物理通讯. 1997, 27(1): 41-48.

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  We numerically show the changing of eigenstates of the Hamiltonian as a function of a control parameter governing the strength of a non-integrable perturbation. The eigenstates change abruptly at avoided level crossing. After the avoided level crossing, they tend to restore their original form before the avoided level crossing, and exchange their distribution, especially for those which can be treated as isolated two-body collisions. But in general, the eigenstates have some changings after the avoided crossing, and the symmetries of the system are broken down locally at this kind of avoided level crossings.
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  Structure of Light Nuclei on Neutron Drip Line

  Zheng-Da WANG, Xiao-Dong ZHANG, Xiao-Chun WANG, Xiao-Bin WANG

  理论物理通讯. 1997, 27(1): 49-56.

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  In order to extend the conventional shell model (SM) calculation with harmonic oscillator bases to light nuclei on neutron drip line, a self-similar-structure shell model (SSM) is proposed. We do this by a rescaling of both the kinetic and potential energy terms of the harmonic oscillator so that the single-particle orbit in SSM has its own state(orbit)-dependent frequency. Meanwhile, a new method to imitate the Woods-Saxon potential with harmonic oscillator potential is introduced. By the rescaling method and imitation procedure, all light exotic nuclei together with the light stable nuclei are studied in a unified way. The results are in good agreement with experimental data. Furthermore, the puzzle of the unexistence of ⁵He, ^{10Li and 13B is naturaUy explained in SSM.}
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  Feature of Energy Spectra of Three-Identical-Particle Systems in Two-Dimensional Space

  Wen-Ying RUAN, Wen-Fang XIE

  理论物理通讯. 1997, 27(1): 57-60.

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  The Hamiltonian of a model system has been diagonalized numericaUy to obtain the eigenstates and eigenenergies. Three types of permutation symmetries: the antisymmetric, the mixed symmetric and the symmetric symmetries have been covered. The dynamical parameters (i.e., the particle mass and the particle-particle interaction) are taken appropriately for a particles, however a series ,of qualitative features are revealed to be iden tical with those of quantum dot electronic systems in semiconductor heterojunctions. We stress the importance of quantum mechanical symmetries in the understanding of quantum mechanical few-body systems.
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  Nambu-Jona-Lasinio Model Beyond the Mean-Field Approximation

  H. GUO, W. Z. DENG, H. X. YE, L. M. YANG

  理论物理通讯. 1997, 27(1): 61-66.

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  1. Department of Technical Physics, Peking University, Beijing 100871, China;
  2. Department of Physics, Peking University, Beijing 100871, China
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  The Structure of ^131,133Xe and the Spin(6) Symmetry

  G. L. LONG, Y. SUO

  理论物理通讯. 1997, 27(1): 67-70.

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  The positive-parity states of ^131,133Xe are studied in the Spin(6) limit of the interacting boson-fermion model. It is found that the main structures in the spectrum and the E2 data can be described in this dynamical symmetry.
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  ΔI= 4 Bifurcation and the sdg Interacting Boson Model

  Yu-Xin LIU, Hong-Zhou SUN, En-Guang ZHAO

  理论物理通讯. 1997, 27(1): 71-76.

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  We show that the superdeformed nuclear states can be described in the framework of the interacting boson model (IBM) with the g-bosons being taken into account in this paper.The ΔI= 4 bifurcation in superdeformed rotational bands can be reproduced in the SU(5) limit of the sdg IBM. The perturbation causing the ΔI= 4 bifurcation to emerge in the ΔI= 2 superdeformed rotational band may possess the SU(5) symmetry.
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  Renormalization Group Analyses of Particle Masses in Full Four-Generation Fermion Condensate Scheme

  Bang-Rong ZHOU

  理论物理通讯. 1997, 27(1): 77-86.

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  It is shown by general arguments and numerical calculations that the mass relation among the top-quark and the fourth generation of Dirac quark-leptons in the full four-generation condensate scheme of the minimal electroweak symmetry breaking could be made rather stable for variation of the compositeness boundary conditions if the fourth generation is assumed to be mass-degenerate in the bubble approximation and the mass equation of the top-quark is used. The perturbative theory is argued to be applicable in most part of the momentum region below the compositeness scales even if these scales are now lower. Thus if the scheme works, then the resulting mass predictions of the fourth generation of quarkleptons leptons and the Higgs sboson from the experimental top-quark mass as an input would be reliable and also insensitive to thepossible range 170 GeV-190 GeV of the top-quark mass.
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  Derivation of Discrete Symmetric Transformations of Quantum Fields in View of the Linear Quantum Transformation Theory

  Yong-De ZHANG, Lei MA

  理论物理通讯. 1997, 27(1): 87-92.

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  In this paper, by using the linear quantum transformation theory (LQT), we derive all of the expressions of discrete symmetric transformations C, P and T for scalar field, electromagnetic field and Dirac field, respectively. So the superiority of LQT is showed here.
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  Three-Poincare Algebra in Complex General Relativity

  Sze-Shiang FENG, Yi-Shi DUAN

  理论物理通讯. 1997, 27(1): 93-100.

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  We obtain a general covariant conservation law of energy momentum in complex general relativity by general displacement transformation in terms of Ashtekar new variables. The energy is exactly the ADM Hamiltonian on the constraint surface on condition that an appropriate time function is chosen. The energy momentum is gauge-covariant and commutes with all the constraints whence they are physical observables. Furthermore, the Poisson brackets of the momentum and the internal SU(2) charges form a three-Poincare algebra.
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  CP Asymmetry in Top Quark-Pair Production via Photon Fusion:(Ⅱ) For Polarized Photon Beams

  Wen-Gan MA, Chao-Hsi CHANG, Xue-Qian LI, Zeng-Hui YU, Liang HAN

  理论物理通讯. 1997, 27(1): 101-104.

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  The effects of CP asymmetry in top-pair production with polarized photon beam collisions,which may arise in two Higgs doublet extensions of the minimal standard model, are studied.Some of the advantages to observe the CP non-invariance in the production are pointed out.The CP asymmetry will be enhanced by polarized photon fusion greatly compared to the unpolarized one and the signal can reach so high up to a few percents.
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  Multimode Boson'Realization of SU(1,l) Lie Algebra Gained via IWOP Technique

  Hong-Yi FAN, Yue FAN

  理论物理通讯. 1997, 27(1): 105-108.

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  We show that the technique of integration within an ordered product (IWOP) of operators provides us with an approach for deriving the disentangling of the multimode boson realization of SU(1,l) coset element. A new type of generalized squeezed states can thus be constructed.
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  A (2+1)-Dimensional Integrable sinh-Gordon Extension

  Qi-Xian WU, Sen-Yue LOU

  理论物理通讯. 1997, 27(1): 109-112.

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  In this letter, we point out that if there is a (2+1)-dimensional extension of the KdV equation,then we can get a corresponding (2+1)-dimensional sine-Gordon (SG) or sinh-Gordon (SHG) extension which is related to the negative flow equation of the KdV extension. The (2+1)-dimensional SG (or SHG) extensions related to the KP, breaking soliton and Nizhnik-Novikov-Veselov equations are known in literature while the (2+1)-dimensional SHG extension related to the negative Aow equation of the Boiti-Leon-Manna-Pempinelli (BLMP) equation is obtained in this letter thanks to the Schwartz form of the BLMP equation being conformal invariant.
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  Nuclear Effect on the Nucleon Structure Function

  Da-Li XUE, Guang-Lie LI

  理论物理通讯. 1997, 27(1): 113-116.

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  The overlap and the leakage of the parton was considered so that the nucleon effective mass can be successfully used as the only free parameter to adjust the structure function ratios recently measured by NMC.
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  Unconventional Medium Effect in K⁺-and π⁺-Nucleus Scattering

  Chong-Hai CAI, Hong SHEN, Ping-Zhi NING, En-Guang ZHAO

  理论物理通讯. 1997, 27(1): 117-120.

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  The ratios of total cross section of K⁺-nucleus to K⁺-deuterium at 400 MeV/c≤pk≤800 MeV/c for ⁶Li, ¹²C, ²⁸Si, ⁴⁰Ca and the differential cross section of π⁺-¹²C scattering at p_π= 800 MeV/c are calculated by taking into account the unconventional medium effect.An enhancement of both the K⁺-and π⁺-nucleus scattering cross sections is obtained.
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  The Problem of Gauge Invariance in the Current Study of Nucleon Spin

  Xiang-Song CHEN, Fan WANG

  理论物理通讯. 1997, 27(1): 121-124.

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  Instead of the popular gauge-dependent decomposition of the total angular momentum operator in QCD, we derived a gauge-invarian t one with better classical correspondence. We also explored the possibility that the requirement of gauge invariance and classical correspondence wiU partly contradict with the commutation relationship of momentum and angular momentum.
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  The Decay of Z→3γ via Charged Higgs Boson Loops in Some Nonstandard Models

  MaeZhi YANG, Xian-Jian ZHOU

  理论物理通讯. 1997, 27(1): 125-128.

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  The fourth rank polarization tensor and the helicity amplitudes of Z→3γ via charged Higgs boson loops in some nonstandard models with more than one Higgs doublet are calculated by using a nonlinear Re gauge. The results are presented in terms of three transcendental functions of B(x), T(x) and I(x, y). We have checked the analytic results in Ref.[6] in comparison with ours.