摘要：
We verify the QED Ward identity for the two- and three-point functions at non-equilibrium in the hard thermal loop (HTL) limit. We use the Keldysh formalism of real time finite temperature field theory. We obtain an identity of the same form as the Ward identity for a set of one loop self-energy and one loop three-point vertex diagrams which are constructed from HTL effective propagators and vertices.
摘要：
We study n-point functions at finite temperature in the closed time path formalism. With the help of two basic column vectors and their dual partners we derive a compact decomposition of the time-ordered n-point functions with 2(n) components in terms of 2(n-1) - 1 independent retarded/advanced n-point functions. This representation greatly simplifies calculations in the real-time formalism.
期刊：
Physica A-Statistical Mechanics and its Applications,1998年252(3-4):417-427 ISSN：0378-4371
通讯作者：
Jia, Y
作者机构：
[Jia, Y] Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;CCAST, World Lab, Beijing 100080, Peoples R China.;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Jia, Y] H;Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
摘要：
A stochastic system with colored correlation between white noise and colored noise is investigated theoretically. A general Fokker-Planck equation of the system is derived by using a standard method. We discuss a bistable system with colored correlation between additive white noise and multiplicative colored one. It is found that the effects of the correlation time of multiplicative colored noise on the statistical properties of the bistable system are different from those of the correlation time of the correlation between additive white noise and multiplicative colored noise on the statistical properties of the bistable system. (C) 1998 Elsevier Science B.V. All rights reserved.
关键词：
Correlation Function;Parameter Study;Source Model;High Emissivity;Fluid Element
摘要：
The Yano-Koonin-Podgoretskiǐ (YKP) parametrisation of Hanbury Brown-Twiss (HBT) two-particle correlation functions opens new strategies for extracting the emission duration and testing the longitudinal expansion in heavy-ion collisions. Based on the recently derived model-independent expressions, we present a detailed parameter study of the YKP parameters for a finite, hydrodynamically expanding source model of heavy-ion collisions. For the class of models studied here, we show that the three YKP radius parameters have an interpretation as longitudinal extension, transverse extension and emission duration of the source in the YKP frame. This frame is specified by the fourth fit parameter, the Yano-Koonin velocity which describes to a good approximation the velocity of the fluid element with highest emissivity and allows to test for the longitudinal expansion of the source. Deviations from this interpretation of the YKP parameters are discussed quantitatively.
作者机构：
[Hu, XM; Peng, JS] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
Using the 'dressed-atom-dressed-mode' approach and separating the decoupled atomic state, we investigate the statistical properties of a quantum-beat laser without inversion. While the fluctuations of the relative amplitude and phase are retained at their vacuum noise levels, the intensity fluctuations in the sum mode are reduced below the shot noise limit with an optimum Mandel parameter Q = -1/2 when the laser is operated well above threshold. In particular, we show that the decoupled atomic state significantly relaxes the parameter requirement for squeezing. The physical cause is also explained.
作者机构：
[Hu, XM; Peng, JS] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
A cascade system can produce lasers with and without inversion simultaneously. Lasing without inversion is maintained by two-photon coherence. Here we examine the quantum statistical properties of cascade lasers from a four level atomic system with two incoherent steps. It is shown that cascade lasers with and without inversion may simultaneously exhibit sub-Poissonian statistics. The intensity fluctuation spectrum in each laser field is reduced up to 25% below the shot noise limit. The succession of the two incoherent steps is responsible for noise reduction. At the same time, we investigate the fluctuation spectrum in the output intensity difference. For a broad range of parameters, up to 50% squeezing is achieved. The physical mechanism is attributed to the ac-Stark effect. In particular, when the present four-level system is reduced to the three-level system, up to 50% squeezing is retained. (C) 1998 Elsevier Science B.V. All rights reserved.
摘要：
A factorial-moment analysis with real (integer and non-integer) phase space partition is applied to pi(+)p and K(+)p collisions at 250 GeV/c. Clear evidence is shown for self-affine rather than self-similar power-law scaling in multiparticle production. The three-dimensional self-affine second-order scaling exponent is determined to be 0.061 +/- 0.010. (C) 1998 Elsevier Science B.V. All rights reserved.
作者机构：
[Li, YD; Liu, LS] Hua Zhong Normal Univ, Inst Particle Phys, Wuhan 430070, Peoples R China.
通讯机构：
[Li, YD] H;Hua Zhong Normal Univ, Inst Particle Phys, Wuhan 430070, Peoples R China.
关键词：
J/psi photoproduction;quark fragmentation
摘要：
The J/psi, photoproduction via resolved photon process at HERA is studied. it turns out that the J/psi production is dominated by the leading order production process in low p(t) range (p(t) < 4 GeV), while in the high p(t) range (p(t) > 4 GeV), it is dominated by the fragmentation processes. The difference of J/psi cross section caused by using GRV and DO photon structure functions is large, especially in the large negative rapidity range. Hence it is possible to use the J/psi photoproduction process to probe the parton distribution of photon and proton, as well as to test the gluon and heavy quark fragmentation of J/psi, from the perturbative QCD.
