Real-time nonequilibrium dynamics in hot QED plasmas: dynamical renormalization group approach

We study the real-time nonequilibrium dynamics in hot QED plasmas implementing a dynamical renormalization group and using the hard thermal loop (HTL) approximation. The focus is on the study of the relaxation of gauge and fermionic mean fields and on the quantum kinetics of the photon and fermion distribution functions. For semihard photons of momentum eT ≪ k ≪ T we find to leading order in the HTL that the gauge mean field relaxes in time with a power law as a result of infrared enhancement of the spectral density near the Landau damping threshold. The distribution function of semihard photons in linear response also relaxes with a power law, with a power that is twice that for the mean field. The dynamical renormalization group reveals the emergence of detailed balance for microscopic time scales larger than 1/k while the rates are still varying with time. The quantum kinetic equation for the photon distribution function allows us to study photon production from a thermalized quark-gluon plasma (QGP) by off-shell effects. We find that for a QGP of temperature T ∼ 200 MeV and lifetime 10 ∼ t ∼ 50 fm/c the hard (k ∼ T ) photon production from off-shell bremsstrahlung (q → qγ and q̄ → q̄γ) at O(α) grows logarithmically in time and is comparable to that produced from on-shell Compton scattering and pair annihilation at O(ααs). Hard fermion mean fields relax as e−αT t ln(ωP t) with ωP = eT/3 the plasma frequency, as a consequence of the emission and absorption of soft magnetic photons. A quantum kinetic equation for hard fermions is obtained directly in real time from a field theoretical approach improved by the dynamical renormalization group. The collision kernel is time-dependent and infrared finite. In linear response the fermion distribution function relaxes with an anomalous exponential law with an exponent twice as large as that for the mean field. Typeset using REVTEX 1