摘要：
We derive a generalized Ward identity for color-superconducting quark matter via the functional integral approach. The identity implies the gauge independence of the color-superconducting gap parameter on the quasiparticle mass shell to subleading order in the covariant gauge.
摘要：
We present a simple set of rules for obtaining the imaginary part of a self-energy diagram at finite temperature as a product of tree amplitudes. These diagrams correspond to physical scattering amplitudes.
摘要：
We study the nonlinear response in weakly coupled hot φ4 theory. We obtain an expression for a quadratic shear viscous response coefficient using two different formalisms: transport theory and response theory. The transport theory calculation is done by assuming a local equilibrium form for the distribution function and expanding in the gradient of the local four dimensional velocity field. By performing a Chapman-Enskog expansion on the Boltzmann equation we obtain a hierarchy of equations for the coefficients of the expanded distribution function. To do the response theory calculation we use Zubarev’s techniques in nonequilibrium statistical mechanics to derive a generalized Kubo formula. Using this formula allows us to obtain the quadratic shear viscous response from the three-point retarded Green function of the viscous shear stress tensor. We use the closed time path formalism of real time finite temperature field theory to show that this three-point function can be calculated by writing it as an integral equation involving a four-point vertex. This four-point vertex can in turn be obtained from an integral equation which represents the resummation of an infinite series of ladder and extended-ladder diagrams. The connection between transport theory and response theory is made when we show that the integral equation for this four-point vertex has exactly the same form as the equation obtained from the Boltzmann equation for the coefficient of the quadratic term of the gradient expansion of the distribution function. We conclude that calculating the quadratic shear viscous response using transport theory and keeping terms that are quadratic in the gradient of the velocity field in the Chapman-Enskog expansion of the Boltzmann equation is equivalent to calculating the quadratic shear viscous response from response theory using the next-to-linear response Kubo formula, with a vertex given by an infinite resummation of ladder and extended-ladder diagrams.
摘要：
We study quadratic response in weakly coupled nonequilibrium phi (4) theory in the context of both classical transport theory and real time quantum field theory. A novel connection between these two approaches is established which provides a diagrammatic interpretation of quadratic shear viscous response. (C) 2001 Elsevier Science B.V. All rights reserved.
摘要：
We derive spectral representations for the different components of the four-point function at finite temperature in the real time formalism in terms of five real spectral densities. We explicitly calculate all these functions in QED in the hard thermal loop approximation. The Ward identities obeyed by the one-loop three- and four-point functions in real time and their spectral functions are derived. We compare our results with those derived previously in the imaginary-time formalism for retarded functions in hot QCD, and we discuss the generalization of our results to non-equilibrium situations.
摘要：
We study the 4-point function in the Keldysh formalism of the closed time path formulation of real time finite temperature field theory. We derive the KMS conditions for these functions and discuss the number of 4-point functions that are independent. We define a set of “physical” functions which are linear combinations of the usual Keldysh functions. We show that these functions satisfy simple KMS conditions. In addition, we consider a set of integral equations which represent a resummation of ladder graphs. We show that these integral equations decouple when one uses the physical functions that we have defined. We discuss the generalization of these results to QED.
作者机构：
[Zhang, BW; Li, JR; Hou, DF] Hua Zhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Zhang, BW] H;Hua Zhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
摘要：
We investigate the self-consistency condition (SCC) of mean-field theory in the Walecka model and find that the solutions of the SCC are multiple at high temperature and chemical potential. Using the effective Lagrangian approach, we study medium effects on the ω meson mass by taking into account vacuum effects. We show that the ω meson mass decreases with both temperature and chemical potential with a general tendency, while near the critical point several ω meson masses degenerate due to the multiple solutions of the SCC. We check the validity of the Brown-Rho scaling law in this case. Finally, we calculate the thermodynamic potential and prove that the multiple solutions of the SCC result from a first-order phase transition of nuclear matter in the Walecka model at high temperature and chemical potential.
作者机构：
[Zhang, BW; Li, JR; Hou, DF] Hua Zhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Zhang, BW] H;Hua Zhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
关键词：
meson mass;vacuum effects;ρNN interaction;scaling law
摘要：
We studied the medium effects on rho meson mass by taking account of the vacuum effects with the effective Lagrangian approach. We show that the rho meson mass decreases with both temperature and chemical potential. Then we checked the validity of Brown-Rho scaling law in different conditions.
摘要：
We study shear viscosity in weakly coupled hot φ4 theory using the closed time path formalism (CTP) of real time finite temperature field theory. We show that the viscosity can be obtained as the integral of a three-point function. Although the three-point function has seven components in the CTP formalism, we show that the viscosity is given by a decoupled integral equation which involves only one retarded three-point function. Non-perturbative corrections to the bare one loop result can be obtained by solving a Schwinger-Dyson type integral equation for this vertex. This integral equation represents the resummation of an infinite series of ladder diagrams which all contribute to the leading order result. It can be shown that this integral equation has exactly the same form as the Boltzmann equation. We show that the integral equation for the viscosity can be reexpressed by writing the vertex as a combination of polarization tensors. An expression for this polarization tensor can be obtained by solving another Schwinger-Dyson type integral equation. This procedure results in an expression for the viscosity which represents a non-perturbative resummation of contributions to the viscosity which includes certain non-ladder graphs, as well as the usual ladders. We discuss the significance of this set of graphs. We show that these resummations can also be obtained by writing the viscosity as an integral equation involving a single four-point function. Finally, we show that when the viscosity is expressed in terms of a four-point function, it is possible to further extend the set of graphs included in the resummation by treating vertex and propagator corrections self-consistently. We discuss the significance of such a self-consistent resummation and show that the integral equations that are involved contain cancellations between vertex and propagator corrections. Lastly, we discuss the prospect of generalizing our technique to gauge theories.
摘要：
We construct a program to calculate Feynman amplitudes at finite temperature in the real time Keldysh formalism using the symbolic manipulation program MATHEMATICA. As an example, the usefulness of this program is demonstrated by proving the finite temperature Ward identity for QED in a second order effective theory.
作者机构：
[Zheng, XP] Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;Zhongshan Univ, Dept Phys, Canton 510275, Peoples R China.
通讯机构：
[Zheng, XP] H;Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
摘要：
We have studied the effect of the third-order density fluctuations in the medium on the collective excitations in quark-gluon plasma. We show that the nonlinear response of a quark-gluon plasma medium leads to non-Abelian collective excitations. We present two kinds of non-Abelian oscillation solutions which respectively correspond to weakly and strongly nonlinear coupling of field components in the color space. We also show that the weakly nonlinear solution is similar to the Abelian-like one but has a frequency shift, which is of order g2T, from the eigenfrequency.
作者机构：
[Li, JR; Zuo, J; Hou, DF] Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hou, DF] H;Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
关键词：
散射过程;初态;有限温度;媒体
摘要：
This letter addresses a problem concerning temperature corrections to the scattering processes. Although former studies had given the temperature-dependent phase space factors in the corrections, how to derive them from the first principles was not clear. In this letter, we consider this question within the formalism of thermal field dynamics. We find that if the initial and final states in scattering processes at finite temperature are constructed from the expanded vacuum states, the scattering rate in medium can be derived with the desired temperature-dependent phase space factors.
通讯机构：
[Hou, DF] H;Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
关键词：
费籽系统;有限温度;谱密度;量子色动力学
摘要：
The pressure of a fermion system is expressed as a mass integral over the full two-point spectral densities within the real time formalism by use of the Keldysh representation for the propagators. This simplifies the calculation significantly and allows a Dyson resummation. The expression is used to demonstrate that potential infrared divergences are rendered harmless. We apply it to check the pressures of an ideal fermion gas and of a chemically non-equilibrated quantum chromodynamics plasma.
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.
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：
The dimensional regularization is applied to three-loop vacuum graphs in massless QED to evaluate temperature-dependent ultraviolet divergences and infrared divergences in arbitrary covariant gauge. They both are shown to be absent due to cancellations among themselves, and the cancellations are gauge-independent although the individual divergences are gauge-dependent.
作者机构：
[Li, JR; Hou, DF] HUA ZHONG NORMAL UNIV,INST PARTICLE PHYS,WUHAN 430070,PEOPLES R CHINA.
通讯机构：
Inst. für Theoretische Physik, Germany
摘要：
By considering the Debye screening and the damping rate of gluons, the viscosity coefficient of the quark-gluon plasma was evaluated via real-time finite temperature QCD in the relaxation time approximation at finite temperature and chemical potential. The results show that both the damping rate and the quark chemical potential cause considerable enhancements to the viscosity coefficient of the hot dense quark-gluon plasma. (C) 1997 Elsevier Science B.V.
通讯机构：
[Hou, DF] H;HUA ZHONG NORMAL UNIV, INST PARTICLE PHYS, WUHAN 430070, PEOPLES R CHINA.
摘要：
We calculate the relaxation time self-consistently to study the damping of collective color modes and the color conductivity in a QGP by deriving self-consistent equations for the damping rates of gluons and quarks to leading order QCD by thermal field dynamics including a chemical potential for quarks. We show that the damping rates are not sensitive to the chemical potential whereas color conductivity is enhanced considerably.
