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Soft photons and hard thermal loops

Francois Gelis
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Abstract

We calculate within the Hard Thermal Loop expansion the production rate of soft photons and lepton pairs by a hot quark-gluon plasma at thermal equilibrium, up to the 2-loop order. Strong collinear divergences appear to mix the orders of the perturbative expansion so that the 2-loop order is in fact dominant compared to the 1-loop order. More precisely, angular integrals that would otherwise be of order 1 are found to behave as powers of $1/g$ when the produced photon is massless, therefore breaking the standard HTL power counting rules.

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Francois Gelis. 1997-10-01. Soft photons and hard thermal loops. https://arxiv.org/abs/hep-ph/9710203

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