# Quark Matter 2018

May 13 – 19, 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

## Second-order transport coefficients at NLO in pQCD

May 15, 2018, 10:00 AM
20m
Sala Volpi, 1st Floor (Palazzo del Casinò)

### Sala Volpi, 1st Floor

#### Palazzo del Casinò

Parallel Talk QCD at high temperature

### Speaker

Jacopo Ghiglieri (CERN)

### Description

In this talk we will study the relaxation coefficients $\tau_\pi$ and $\tau_J$ of the shear stress tensor $\pi^{\mu\nu}$ and the light quark current $J$ respectively. These are second-order transport coefficients which can be determined in perturbation theory. After reviewing the perturbative kinetic theory framework that has been recently used to determine their respective first-order coefficients $\eta$ and $D$ (shear viscosity and quark diffusion) at NLO in pQCD we will apply it to these second-order coefficients. While $\eta$ and $D$ get reduced by a factor of 5 at NLO for $\alpha_\mathrm{s}\sim0.3$, the dimensionless ratios $T \tau_\pi/(\eta/s)$ and $\tau_J/D$ show a mild increase ($<50\%$) at NLO. We further argue that, through the properties of the collision operator, lower bounds can be obtained in kinetic theory for these coefficients. After presenting the bounds, we compare our results with the strong-coupling AdS/CFT ones: we argue that, while (NLO) kinetic theory can yield first-order transport coefficients in the ballpark of the strong-coupling ones, the lower bounds imply widely different behaviours at second order.

Centralised submission by Collaboration Presenter name already specified Theory

### Primary authors

Jacopo Ghiglieri (CERN) Derek Teaney (Stony Brook University) Prof. Guy Moore (TU Darmstadt)