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arXiv 0709.0323hep-ph
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用HTL改进的梯形Dyson-Schwinger方程分析热QED/QCD的相结构--关于解的规范依赖性

Analysis of the Phase Structure of Thermal QED/QCD through the HTL Improved Ladder Dyson-Schwinger Equation --On the Gauge Dependence of the Solution--

Hisao Nakkagawa, Hiroshi Yokota, Koji Yoshida

摘要:

为了研究热QCD/QED中费米子质量的自发产生,我们用数值方法求解了滞后费米子自能函数$Σ_R$的HTL改进的梯形DS方程,并研究了在一般协变规范下,当规范参数$ξ$为任意常数时,该方程解的规范依赖性.利用所得到的数值解,我们发现:i)费米子波函数重整化函数$A(P)$即使在定义了质量的动量下也总是偏离1,因此相应的解与Ward-Takahashi恒等式明显矛盾。ii)结果表明,所得到的解强烈依赖于规范参数的选择:临界温度和临界耦合常数随规范的变化而变化。在我们研究的所有规范中,我们都找不到任何解,有可能与Ward-Takahashi恒等式一致。因此我们不得不研究如何找到一个能使我们得到与Ward-Takahashi恒等式一致的解的规范,否则无论如何改进规范传播子,我们都不能通过对点-顶点梯形DS方程的分析得到任何物理上合理的结论。

英文摘要:

We solved with a numerical procedure the HTL improved ladder DS equation for the retarded fermion self-energy function $Σ_R$ to study the spontaneous generation of fermion mass in thermal QCD/QED, and studied the gauge-dependence of the solution within a general covariant gauge where the gauge parameter $ξ$ is any constant number. With the numerical solutions thus obtained, we found the followings; i) The fermion wave function renormalization function $A(P)$ always deviates largely from unity even at the momentum where the mass is defined, thus the corresponding solutions explicitly contradict with the Ward-Takahashi identity. ii) As a result, the obtained solutions strongly depend on the choice of gauge parameters: the critical temperatures and the critical coupling constants significantly change gauge by gauge. In all gauges we studied in the present analysis, we could not find any solution, having a possibility to be consistent with the Ward-Takahashi identity. Thus we are forced to investigate the procedure to find a gauge which enables us to get a solution being consistent with the Ward-Takahashi identity, otherwise we can not obtain any physically sensible conclusions through the analysis of the point-vertex ladder DS equation no matter how the gauge propagator gets improved.

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