Are gluon showers inside a QGP strongly or weakly coupled ? a theorist's test

Jets produced from colliding two heavy nuclei play an important role in un-

derstanding properties of the Quark Gluon Plasma. During their travel through

the medium, high energy partons lose energy through splitting processes like

bremsstrahlung and pair production, induced by elastic scatterings with the

medium. In the high energy limit, these splitting processes are coherent over

large distances and the underlying elastic scatterings can no longer be treated

as quantum mechanically independent, leading to a suppression of the splitting

rate known as the Landau-Pomeranchuk-Migdal effect. An important question

is whether consecutive splittings are themselves quantum mechanically indepen-

dent or instead overlap significantly. Previously, the overlap of splitting rates

has been calculated in the soft bremsstrahlung limit and it was found that such

corrections are large but can be absorbed by accounting for similar corrections

to a qˆ parameter that characterises properties of the medium. Since we now

have the QCD calculations required, we can answer the refined question: how

big are the corrections to shower development due to overlapping formation

times that cannot be absorbed into an effective value of qˆ ?