Lattice constraints on the thermal photon rate

TL;DR

This study estimates the thermal photon production rate in an SU(3) plasma near the critical temperature using lattice QCD results, spectral function analysis, and comparisons with perturbative and holographic models, revealing consistency with weak-coupling predictions at high momenta.

Contribution

It provides a lattice-based estimation of the photon rate near Tc, incorporating continuum extrapolation and spectral function interpolation, bridging non-perturbative and perturbative approaches.

Findings

Photon rate at high momenta (~3T) aligns with NLO weak-coupling predictions.

Uncertainties increase at lower momenta (~2T), suggesting a transition to strongly interacting behavior.

Spectral function analysis supports the hydrodynamic regime at small invariant masses.

Abstract

We estimate the photon production rate from an SU(3) plasma at temperatures of about 1.1Tc and 1.3Tc. Lattice results for the vector current correlator at spatial momenta k ~ (2-6)T are extrapolated to the continuum limit and analyzed with the help of a polynomial interpolation for the corresponding spectral function, which vanishes at zero frequency and matches to high-precision perturbative results at large invariant masses. For small invariant masses the interpolation is compared with the NLO weak-coupling result, hydrodynamics, and a holographic model. At vanishing invariant mass we extract the photon rate which for k \gsim 3T is found to be close to the NLO weak-coupling prediction. For k \lsim 2T uncertainties remain large but the photon rate is likely to fall below the NLO prediction, in accordance with the onset of a strongly interacting behaviour characteristic of the hydrodynamic regime.