Photon production from a thermalized quark gluon plasma: quantum kinetics and nonperturbative aspects

Abstract

We study the production of photons from a quark gluon plasma in local thermal equilibrium by introducing a non-perturbative formulation of the real time evolution of the density matrix. The main ingredient is the real time effective action for the electromagnetic field to $\mathcal{O}({\alpha }_{em})$ and to all orders in ${\alpha }_s$. The real time evolution is completely determined by the solution of a \emph{classical stochastic} non-local Langevin equation which provides a Dyson-like resummation of the perturbative expansion. The Langevin equation is solved in closed form by Laplace transform in terms of the thermal photon polarization. A quantum kinetic description emerges directly from this formulation. We find that photons with $k\lesssim 200Mev$ \emph{thermalize} as plasmon quasiparticles in the plasma on time scales $t\sim 10-20fm/c$ which is of the order of the lifetime of the QGP expected at RHIC and LHC. We then obtain the direct photon yield to lowest order in ${\alpha }_{em}$ and to leading logarithmic order in ${\alpha }_s$ in a \emph{uniform} expansion valid at all time. The yield during a QGP lifetime $t\sim 10fm/c$ is systematically larger than that obtained with the equilibrium formulation and the spectrum features a distinct flattening for $k\gtrsim 2.5Gev$. We discuss the window of reliability of our results, the theoretical uncertainties in \emph{any} treatment of photon emission from a QGP in LTE and the shortcomings of the customary S-matrix approach.

31 pages. To appear in Nucl. Phys. A. New section (VII) with response to and criticism of hep-ph/0312222

References in corpus (5)

• Azimuthal anisotropy and correlations in the hard scattering regime at RHIC
• Dynamical renormalization group approach to relaxation in quantum field theory
• Emission of thermal photons and the equilibration time in Heavy-Ion collisions
• Dynamical renormalization group approach to transport in ultrarelativistic plasmas: the electrical conductivity in high temperature QED
• Are direct photons a clean signal of a thermalized quark gluon plasma?

Cited by in corpus (8)

• Dilepton production from hot hadronic matter in nonequilibrium
• Production of a sterile species via active-sterile mixing: an exactly solvable model
• Non equilibrium dynamics of mixing, oscillations and equilibration: a model study
• Remarks on transient photon production in heavy ion collisions
• Off-equilibrium photon production during the chiral phase transition
• Direct Photons from Hot Quark Matter in Renormalized Finite-Time-Path QED
• Asymptotic description of finite lifetime effects on the photon emission from a quark-gluon plasma
• Production of a sterile species: quantum kinetics