Thermal dilepton rates and electrical conductivity of the QGP from the lattice

TL;DR

This study uses lattice QCD to analyze the temperature dependence of dilepton rates and electrical conductivity in the quark-gluon plasma, finding near temperature independence and quantifying conductivity at various temperatures.

Contribution

It provides a non-perturbative lattice QCD calculation of the spectral functions, dilepton rates, and electrical conductivity of the QGP at different temperatures, with systematic uncertainty analysis.

Findings

Electrical conductivity ranges from 0.2 to 0.7 times C_em at T=1.1T_c

Dilepton and photon rates show negligible temperature dependence

Vector correlation functions are nearly temperature independent in the studied range

Abstract

We investigate the temperature dependence of the thermal dilepton rate and the electrical conductivity of the gluon plasma at temperatures of $1.1T_c$, $1.3T_c$ and $1.5T_c$ in quenched QCD. Making use of non-perturbatively clover-improved Wilson valence quarks allows for a clean extrapolation of the vector meson correlation function to the continuum limit. We found that the vector correlation function divided by $T^3$ is almost temperature independent in the current temperature window. The spectral functions are obtained by $\chi^2$ fitting of phenomenologically inspired Ans\"atze for the spectral function to the continuum extrapolated correlator data, where the correlations between the data points have been included. Systematic uncertainties arising from varying the Ans\"atze motivated from strong coupling theory as well as perturbation theory are discussed and estimated. We found that the electrical conductivity of the hot medium, related to the slope of the vector spectral function at zero frequency and momentum, is $0.2C_{em}\lesssim \sigma/T\lesssim0.7C_{em}$ for $T=1.1T_c$ and $0.2C_{em}\lesssim \sigma/T\lesssim0.4C_{em}$ for the higher temperatures. The dilepton rates and soft photon rates, resulting from the obtained spectral functions, show no significant temperature dependence, either.