Dilepton and photon production in the presence of a nontrivial Polyakov loop

TL;DR

This paper investigates how a nontrivial Polyakov loop affects dilepton and photon production in the semi-QGP near the deconfinement transition, revealing a mild enhancement for dileptons and a strong suppression for photons.

Contribution

It provides the first leading-order calculation of dilepton and photon production rates in the semi-QGP, accounting for Polyakov loop effects and their impact on different production mechanisms.

Findings

Dilepton production is mildly enhanced (~20%) in the semi-QGP.

Photon production is strongly suppressed by about an order of magnitude.

The two-photon production mechanisms are affected differently by the Polyakov loop.

Abstract

We calculate the production of dileptons and photons in the presence of a nontrivial Polyakov loop in QCD. This is applicable to the semi-Quark Gluon Plasma (QGP), at temperatures above but near the critical temperature for deconfinement. The Polyakov loop is small in the semi-QGP, and near unity in the perturbative QGP. Working to leading order in the coupling constant of QCD, we find that there is a mild enhancement, ~ 20%, for dilepton production in the semi-QGP over that in the perturbative QGP. In contrast, we find that photon production is strongly suppressed in the semi-QGP, by about an order of magnitude, relative to the perturbative QGP. In the perturbative QGP photon production contains contributions from 2->2 scattering and collinear emission with the Landau- Pomeranchuk-Migdal (LPM) effect. In the semi-QGP we show that the two contributions are modified differently. The rate for 2->2 scattering is suppressed by a factor which depends upon the Polyakov loop. In contrast, in an SU(N) gauge theory the collinear rate is suppressed by 1/N, so that the LPM effect vanishes at infinite N. To leading order in the semi-QGP at large N, we compute the rate from 2->2 scattering to the leading logarithmic order and the collinear rate to leading order.