Testing thermal photon and dilepton rates

TL;DR

This paper compares next-to-leading order thermal vector spectral functions with lattice QCD data at high temperature, revealing that the spectral function is lower than perturbative predictions in certain frequency ranges, aiding spectral reconstruction efforts.

Contribution

It provides a detailed comparison between NLO perturbative spectral functions and lattice data, incorporating new perturbative results and constraining the strong coupling scale.

Findings

Spectral function falls below NLO predictions in a significant frequency domain.

Lattice data constrains the choice of the strong coupling constant.

Results support previous indications about the spectral function's behavior.

Abstract

We confront the thermal NLO vector spectral function (both the transverse and longitudinal channel with respect to spatial momentum, both above and below the light cone) with continuum-extrapolated lattice data (both quenched and with $N_{\rm f} = 2$, at $T \sim 1.2 T_{\rm c}$). The perturbative side incorporates new results, whose main features are summarized. The resolution of the lattice data is good enough to constrain the scale choice of $\alpha_{\rm s}$ on the perturbative side. The comparison supports the previous indication that the true spectral function falls below the resummed NLO one in a substantial frequency domain. Our results may help to scrutinize direct spectral reconstruction attempts from lattice QCD.