High-Energy Showing inside the QGP: weak vs. strong coupling

Consider a very high-energy parton (E >> T) traveling through a quark-gluon plasma (QGP). The parton can lose energy by showering inside the medium, like a cosmic ray showers in the atmosphere. There are two extremes for picturing such a shower: If we imagine that the running strong coupling is at least moderately small at the relevant energy scale, we can calculate the development of the shower by picturing the shower as a collection of individual high-energy partons that keep splitting via bremsstrahlung and pair production. If we instead imagine that the running strong coupling is very strong, we cannot treat the high-energy partons individually, and we might, for example, turn to AdS/CFT descriptions of the process for qualitative insight. As one increases coupling, when does the (weak-coupling) particle picture of the shower irretrievably break down? In this talk, I will discuss the current status of field theory calculations meant to address that question (in simple situations) by calculating the size of corrections to the weak-coupling picture of high-energy parton showers. The discussion involves investigating what happens when the quantum durations of consecutive splittings of a parton in the shower overlap each other. The calculation requires a significant generalization of the Landau-Pomeranchuk-Migdal (LPM) effect, which plays a roll in the theory of both cosmic ray showers and jets in quark-gluon plasmas.