Nonequilibrium quantum plasmas in scalar QED: Photon production, magnetic and Debye masses, and conductivity - art. no. 085007

We study the generation of a nonequilibrium plasma in scalar QED with N-cha rged scalar fields in the cases (a) of a supercooled second order phase tra nsition through spinodal instabilities and (b) of parametric amplification when the order parameter oscillates with large amplitude around the minimum of the potential. The focus is to study the nonequilibrium electromagnetic properties of the plasma, such as photon production, electric and magnetic screening and conductivity. A novel kinetic equation is introduced to comp ute photon production far away from equilibrium in the large N limit and lo west order in the electromagnetic coupling. During the early stages of the dynamics the photon density grows exponentially and asymptotically the freq uency distribution becomes N-ph(omega) similar to alpha m(2)/[lambda(2)omeg a(3)] with lambda the scalar self-coupling and m the scalar mass. In the ca se of a phase transition, electric and magnetic fields are correlated on di stances xi(t) similar to root (t/m) over bar during the early stages of the evolution and the power spectrum is peaked at low momentum. This aspect is relevant for the generation of primordial magnetic fields in the early Uni verse and for photoproduction as a potential experimental signature of the chiral phase transition. Magnetic and Debye screening masses are defined ou t of equilibrium as generalizations of the equilibrium case. While the magn etic mass vanishes out of equilibrium in this Abelian model, we introduce a n effective time and wave-number dependent magnetic mass that reveals the d ifferent processes that contribute to screening and their time scales. The Debye mass turns out to be m(Deb)(2) similar to alpha m(2)/lambda for a sup ercooled phase transition while in the case of an oscillating order paramet er an interpolating time dependent Debye mass grows as alpha root<(mt/lambd a)over bar> due to a non-linear resonance at low momentum in the charged pa rticle distribution. It is shown how the transverse electric conductivity b uilds up during the formation of the nonequilibrium plasma. Its long wavele ngth limit reaches a value sigma(k approximate to 0) similar to alpha m/lam bda at the end of the stage of linear instabilities. It is shown that the e lectric conductivity stays finite for all k including k = 0 for finite time . In the asymptotic regime it attains a form analogous to the equilibrium c ase but in terms of the nonequilibrium particle distribution functions.