| The Finite-Temperature Field Theory is widely used to investigate the property of quark-gluon plasma. Basing on this theory, in this paper, a new Feyn-man rule for directly calculating the retarded, advanced Green functions and the bremsstrahlung in thermal QED are discussed.We first recall the Closed-Time Path Formalism in real-time finite-temperature field theory and introduce two kinds of representations: single-time representation and physical representation. The physical field, ghost field and matrix propagator are defined in the single-time representation. Type-1 vertex is identical with the physical field vertex, type-2 vertex is different with a opposite sign, external particle line (physical leg) is only connect with the type-1 vertex. In physical representation, the non-vanish components of matrix are retarded, advanced Green function and the matrix component related with the thermal distribution function. Using the Keldysh transformation, we deduce a new Feynman rule in <^3 theory. The advantage is that it can be used to directly calculate the real physics quantities in an economic way. In this way, we needn't perform the analytical continuation from the result in the ITF. This new rule has the following property; the vertex is only related with the coupling constant and independent of the orientation of the momenta, one half of the vertex components vanish. The 2-pointself-energy and 3-point vertex correction in |
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