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Two mechanisms for the elimination of pinch singularities in out of equilibrium thermal field theories

I. Dadic
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Abstract

We analyze ill-defined pinch singularities characteristic of out of equilibrium thermal field theories. We identify two mechanisms that eliminate pinching even at the single self-energy insertion approximation to the propagator: the first is based on the vanishing of phase space at the singular point (threshold effect). It is effective in QED with a massive electron and a massless photon. In massless QCD, this mechanism fails, but the pinches cancel owing to the second mechanism, i.e., owing to the spinor/tensor structure of the single self-energy insertion contribution to the propagator. The constraints imposed on distribution functions are very reasonable.

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I. Dadic. 1999-03-17. Two mechanisms for the elimination of pinch singularities in out of equilibrium thermal field theories. https://doi.org/10.1103/physrevd.59.125012

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