Infrared behavior of the gluon propagator in nonequilibrium situations

Abstract

The infrared behaviour of the medium modified gluon propagator in non-equilibrium situations is studied in the covariant gauge using the Schwinger-Keldysh closed-time path formalism. It is shown that the magnetic screening mass is non-zero at the one loop level whenever the initial gluon distribution function is non isotropic with the assumption that the distribution function of the gluon is not divergent at zero transverse momentum. For isotropic gluon distribution functions, such as those describing local equilibrium, the magnetic mass at one loop level is zero which is consistent with finite temperature field theory results. Assuming that a reasonable initial gluon distribution function can be obtained from a perturbative QCD calculation of minijets, we determine these out of equilibrium values for the initial magnetic and Debye screening masses at energy densities appropriate to RHIC and LHC. We also compare the magnetic masses obtained here with those obtained using finite temperature lattice QCD methods at similar temperatures at RHIC and LHC.

Fermion production in time-dependent fields

“…The general aspects of the exact solution for the momentum spectrum (48) are best seen in figures (3a) and (4). As a function of the transverse momentum k T it peaks once and shows no further relative extrema or other distinct structures.…”

“…It is relevant for the physics of the early universe [1], of intense laser fields [2] as well as of ultra-relativistic heavy-ion collisions and the quark-gluon plasma [3] (QGP). A lot of effort is made to study the QGP's production and equilibration [4] in nuclear collision experiments at the Relativistic Heavy-Ion Collider (RHIC) at the Brookhaven National Laboratory (BNL) and the Large Hadron Collider (LHC) under construction at CERN. The existence of such a state of matter is predicted by lattice QCD calculations at high temperatures [5].…”

Nuclear and quark matter at high temperature

“…In the perturbative QCD approach this term is related to an infrared divergence [67,68], and as such it is independent of UV renormalization schemes. The magnetic gluon mass of order g 2 T seems to be of genuine non-perturbative origin [69,70]. It plays a role also in the calculation of other physically relevant quantities, like shear viscosity.…”

Jet quenching and gluon to hadron fragmentation function in non-equilibrium QCD at RHIC and LHC

“…However, we will directly work with the Faddeev-Popov (F-P) determinant in this paper and we will work in the frozen ghost formalism [8,9] for the medium part at the initial time t = t in = 0. Hence it is now straightforward to extend the generating functional of the scalar gluon in non-equilibrium in eq.…”

“…It should be mentioned, however, that implementing CTP in non-equilibrium at RHIC and LHC is a very difficult problem, especially due to the presence of gluons in non-equilibrium and hadronization etc. Even the calculation of one-loop gluon self energy in non-equilibrium in covariant gauge which is derived in [8,9] becomes much more tedious than the calculation of one loop QCD diagram in vacuum due to the presence of additional closed time path indices in non-equilibrium.…”