Soft Real Photon Productionrate

One of the outstanding problems in QCD at high temperature is the calculation of the soft real photon production rate. The current understanding relies on phenomenological or semiclassical models while the field-theoretical treatments using perturbative first-principle QCD are contradictory. The latter results are plagued with enhancements due to infrared and collinear singularities. In QCD at high temperature all long range forces are screened by medium effects. Thus the above mentioned singularities should be spurious. To avoid them one has to reorganize the conventional perturbation series to include the medium effects consistently. An example is the hard thermal loop (HTL) resummation by Braaten and Pisarski. Recently, an improved HTL resummation scheme has been proposed by Prof. Rebhan and the applicant which is free from collinear singularities. It would be very interesting to apply this scheme to calculate the soft real photon production rate. Up to now it only has been applied to subsets of all contributing Feynman-diagrams. In the complete set it is promising to search for cancellation between enhanced terms by a mechanism close to the Bloch- Nordsieck-theorem at zero temperature.