Photon emission from quark-gluon plasma out of equilibrium

Abstract

The photon emission from a non-equilibrium quark-gluon plasma (QGP) is analyzed. We derive an integral equation that describes photon production through quark-antiquark annihilation and quark bremsstrahlung. It includes coherence between different scattering sites, also known as the LandauPomeranchuk-Migdal effect. These leading-order processes are studied for the first time together in an out-of-equilibrium field theoretical treatment that enables the inclusion of viscous corrections to the calculation of electromagnetic emission rates. In the special case of an isotropic, viscous, plasma the integral equation only depends on three constants which capture the non-equilibrium nature of the medium.

Penetrating probes: Jets and photons in a non-equilibrium quark-gluon plasma

“…which describes quasiparticles with thermal mass m and decay width Γ. Their rr correlator is [5] S rr (P)…”

“…The collision kernel, C, describes the density of mediating gluons that the emitting quark sees. It can be obtained from G rr [5].…”

Direct photon production in relativistic heavy-ion collisions - a theory update

“…However, at leading order and in thermal equilibrium it turns out that S 1122 = 2 f F p 0 + k 0 1 − f F (p 0 ) Re S aarr , where f F is a Fermi-Dirac distribution function. Away from equilibrium, however, a careful analysis of the topology of the Feynman diagrams contributing to the four-point functions shows that [19,21] (at leading order)…”

“…Putting the elements together, one gets the rates for real photon emission from a non-equilibrium medium to be [19,21] ω…”

“…with C F the Casimir operator, m 2 D the non-equilibrium Debye mass, and Ω characterizing the occupation density of soft gluons [19,21]. In an anisotropic plasma, the collision kernel C (q ⊥ ) and its integral, the quark decay width, are formally divergent, owing to gauge field instabilities [23].…”