Photon Emission from a Momentum Anisotropic Quark-Gluon Plasma

TL;DR

This paper calculates photon emission rates from an anisotropic quark-gluon plasma, incorporating off-equilibrium effects, and compares diagrammatic and kinetic approaches to support their equivalence in describing photon production.

Contribution

It introduces a leading-order calculation of photon emission in anisotropic plasmas, proving the KMS relation's validity and comparing two theoretical approaches for accurate phenomenological modeling.

Findings

KMS relation holds for anisotropic distributions in the hard loop regime.

Diagrammatic and kinetic approaches yield consistent photon emission rates.

Provides parameterizations for use in heavy-ion collision studies.

Abstract

We compute the photon emission rate from a quark-gluon plasma with an anisotropic particle momentum distribution induced by a non-vanishing local shear pressure tensor. Our calculation includes photon production through Compton scattering and quark-antiquark annihilation at leading order in $\alpha_s$, with all off-equilibrium corrections to leading order in the momentum anisotropy. For fermions we prove that the Kubo-Martin-Schwinger (KMS) relation holds in the hard loop regime for any particle momentum distribution function that is reflection-symmetric. This supports the equivalence, for 2 to 2 scattering processes, of the diagrammatic and kinetic approaches to calculating the photon emission rate. We compare the viscous rates from these two approaches at weak and realistic coupling strengths and provide parameterizations of the equilibrium and viscous photon emission rates for phenomenological studies in relativistic heavy-ion collisions.