Photon and dilepton production in supersymmetric Yang-Mills plasma

TL;DR

This paper calculates photon and dilepton emission rates in N=4 supersymmetric Yang-Mills plasma at both weak and strong coupling, comparing results with QCD and analyzing spectral functions and electric conductivity.

Contribution

It provides the first non-perturbative strong coupling computation of photon and dilepton production in supersymmetric plasma using AdS/CFT, and compares with weak coupling and QCD results.

Findings

Strong coupling spectral functions show hydrodynamic peaks at low frequency.

Photon emission rates differ systematically between weak and strong coupling.

Electric conductivity is evaluated at strong coupling and leading-log order at weak coupling.

Abstract

By weakly gauging one of the U(1) subgroups of the R-symmetry group, N=4 super-Yang-Mills theory can be coupled to electromagnetism, thus allowing a computation of photon production and related phenomena in a QCD-like non-Abelian plasma at both weak and strong coupling. We compute photon and dilepton emission rates from finite temperature N=4 supersymmetric Yang-Mills plasma both perturbatively at weak coupling to leading order, and non-perturbatively at strong coupling using the AdS/CFT duality conjecture. Comparison of the photo-emission spectra for N=4 plasma at weak coupling, N=4 plasma at strong coupling, and QCD at weak coupling reveals several systematic trends which we discuss. We also evaluate the electric conductivity of N=4 plasma in the strong coupling limit, and to leading-log order at weak coupling. Current-current spectral functions in the strongly coupled theory exhibit hydrodynamic peaks at small frequency, but otherwise show no structure which could be interpreted as well-defined thermal resonances in the high-temperature phase.