ON ANGULAR ORDERING IN MEDIUM-INDUCED RADIATION

As an attempt to understand color coherence effects in medium from first principles, we calculate the double differential spectrum of medium-induced gluon emission off a quark–antiquark antenna in the framework of perturbative QCD. Within this setup we find a soft singularity, analogous to the vacuum spectrum, yet, as opposed to the vacuum, the collinear singularity is regulated by the pair opening angle, leading to a strict anti-angular ordering. We comment on the possible consequences of this new contribution for reconstructed jet observables in heavy-ion collisions.

ANGULAR INTRICACIES IN HOT GAUGE FIELD THEORIES

In hot quantum field theories, "Hard Thermal Loops" leading order calculations call for a definite sequence of angular averages and discontinuity (or Imaginary part prescription) operations, and run otherwise into incorrect results. The ten years old collinear singularity problem of hot QCD, provides a dramatic illustration of that fate.