Abstract: Consider a (nearly-on-shell) high-energy parton (E >> T) traveling through a quark-gluon plasma (QGP), losing 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 theoretical situations) by calculating the size of corrections to the weak-coupling picture of high-energy in-medium 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. The calculation of the main elements needed for this analysis in (large-N) QCD has recently been completed.
on-line via ZOOM