Uncertainty quantification of holographic transport and energy loss for the hot and baryon-dense QGP

TL;DR

This paper uses a new numerical holographic model to quantify uncertainties in transport properties of hot, dense QGP, integrating lattice QCD data and exploring a wide phase diagram including critical points.

Contribution

It introduces a novel numerical method for extracting thermodynamic quantities in holography and applies Bayesian sampling to propagate lattice QCD uncertainties to transport predictions.

Findings

Transport coefficients vary across the phase diagram.

Good agreement with heavy-ion collision estimates at zero density.

Uncertainty propagation covers crossover and critical regions.

Abstract

We investigate several transport coefficients across the phase diagram of a holographic Einstein-Maxwell-Dilaton (EMD) model of hot and dense QCD with $N_f=2+1$ flavors. Our results are obtained from an open-source implementation of this model in C++, publicly available as a module within the MUSES Framework. This code includes a new numerical method to extract thermodynamic quantities from near-boundary asymptotics in holographic models, introduced here for the first time, which greatly improves numerical stability and performance in comparison to earlier implementations. Thanks to this improved technique, we are able to compute results for many realizations of our holographic model, sampled from a Bayesian posterior distribution constrained by lattice QCD results at zero chemical potential. This allows us to propagate lattice QCD error bars to predictions of transport coefficients in a wide window of temperature and baryon chemical potential, covering the crossover region, the neighborhood of the predicted critical point, and the line of first-order phase transition. The physical observables include baryon and thermal conductivities, baryon diffusion, shear and bulk viscosities, the jet-quenching parameter, the heavy-quark drag force, and Langevin diffusion coefficients. At vanishing baryon density, we compare our results to estimates extracted by the JETSCAPE Collaboration from heavy-ion data, with which we find good agreement.