Gauge invariant momentum broadening of hard probes in glasma

TL;DR

This paper calculates the gauge-invariant transverse momentum broadening coefficient of hard probes in the early-stage glasma of heavy-ion collisions, confirming its significant role in jet quenching.

Contribution

It introduces a gauge-invariant method to compute the momentum broadening coefficient, improving upon previous gauge-violating approximations.

Findings

Gauge-invariant results closely match previous simplified calculations.

The glasma significantly contributes to jet quenching.

The method confirms earlier conclusions about glasma's role in momentum broadening.

Abstract

We compute the transport coefficient $\hat q$ which quantifies the transverse momentum broadening of hard probes passing through the evolving glasma from the earliest stage of relativistic heavy-ion collisions. We use a proper-time expansion method which is designed to study the glasma at very early times. In our earlier calculations of $\hat q$ we used an approximation that greatly simplifies the complexity of the calculation but introduces a violation of gauge invariance. Based on these results we argued that the glasma plays an important role in jet quenching. In this paper we have used a gauge invariant formulation to calculate $\hat q$. The results for the momentum broadening coefficient are quantitatively very close to those of our previous simplified version of the calculation and confirm our earlier conclusion about the importance of the glasma contribution to jet quenching.