Energy flow along the medium-induced parton cascade

TL;DR

This paper analyzes the dynamics of medium-induced parton cascades in dense QCD matter, highlighting their energy flow properties, scaling behaviors, and differences from vacuum cascades, with implications for understanding energy transport in high-energy nuclear collisions.

Contribution

It introduces a classification of parton cascades based on their branching rates and explores the unique energy flow and scaling properties of medium-induced cascades.

Findings

Medium-induced cascades exhibit a constant energy flow towards soft modes.

These cascades show wave turbulence-like scaling properties.

Energy accumulates at zero energy in medium-induced cascades, unlike in vacuum cascades.

Abstract

We discuss the dynamics of parton cascades that develop in dense QCD matter, and contrast their properties with those of similar cascades of gluon radiation in vacuum. We argue that such cascades belong to two distinct classes that are characterized respectively by an increasing or a constant (or decreasing) branching rate along the cascade. In the former class, of which the BDMPS, medium-induced, cascade constitutes a typical example, it takes a finite time to transport a finite amount of energy to very soft quanta, while this time is essentially infinite in the latter case, to which the DGLAP cascade belongs. The medium induced cascade is accompanied by a constant flow of energy towards arbitrary soft modes, leading eventually to the accumulation of the initial energy of the leading particle at zero energy. It also exhibits scaling properties akin to wave turbulence. These properties do not show up in the cascade that develops in vacuum. There, the energy accumulates in the spectrum at smaller and smaller energy as the cascade develops, but the energy never flows all the way down to zero energy. Our analysis suggests that the way the energy is shared among the offsprings of a splitting gluon has little impact on the qualitative properties of the cascades, provided the kernel that governs the splittings is not too singular.