Probing the photon emissivity of the quark-gluon plasma without an inverse problem in lattice QCD

TL;DR

This paper presents novel lattice QCD calculations of the photon emissivity of the quark-gluon plasma by directly computing spectral function moments without inverse problems, providing insights into thermal photon production.

Contribution

First lattice QCD results on spectral function moments at lightlike kinematics without inverse problem, advancing understanding of photon emission in quark-gluon plasma.

Findings

Computed moments of the spectral function at T≈250 MeV.

Compared lattice results with weak-coupling dispersive calculations.

Performed continuum limit of the lattice data.

Abstract

The thermal photon emissivity of the quark-gluon plasma is determined by the in-medium spectral function of the electromagnetic current at lightlike kinematics, $\sigma(\omega)$. In this work, we present the first lattice QCD results on moments of $\sigma(\omega)/\omega$, defined by the weight function $1/(\omega^2+ (2\pi T n)^2)$, $n\in\mathbb{Z}$ and computed without encountering an inverse problem. We employ two dynamical flavours of O($a$)-improved Wilson fermions at a temperature $T\approx 250\;$MeV and perform the continuum limit. We compare our results for the first two moments to those obtained dispersively by integrating over the spectral function computed at weak coupling by Arnold, Moore and Yaffe.