Probes of the quark-gluon plasma and plasma instabilities

Penetrating probes in heavy-ion collisions, like jets and photons, are sensitive to the transport coefficients of the produced quark-gluon plasma, such as shear and bulk viscosity. Quantifying this sensitivity requires a detailed understanding of photon emission and jet-medium interaction in a nonequilibrium plasma during the hydrodynamic stages of heavy-ion collisions. Up to now, such an understanding has been hindered by plasma instabilities. These instabilities arise out of equilibrium and lead to spurious divergences when evaluating the rate of interaction of hard probes with the plasma. In this paper, we show that taking into account the time evolution of an unstable plasma cures these divergences. Specifically, we calculate the time evolution of gluon two-point correlators in a setup with a small initial momentum anisotropy and show that the gluon occupation density at first grows exponentially. Based on this calculation, we argue for a phenomenological prescription where instability poles are subtracted. Finally, we show that in the Abelian case instability fields do not affect medium-induced photon emission to our order of approximation.

Automated summary

The sensitivity of penetrating probes in heavy-ion collisions to the transport coefficients of quark-gluon plasma requires a detailed understanding of photon emission and jet-medium interaction in a nonequilibrium plasma. Accounting for the time evolution of an unstable plasma can cure spurious divergences when evaluating the rate of interaction of hard probes with the plasma. The exponential growth of gluon occupation density in an unstable plasma may suggest a phenomenological prescription where instability poles are subtracted. Additionally, instability fields do not seem to affect medium-induced photon emission in the Abelian case to the examined approximation level.