Non-equilibrium photon production arising from the chiral mass shift

TL;DR

This paper studies photon emission during the chiral phase transition in heavy-ion collisions, focusing on mass shifts of quarks and avoiding UV divergences present in earlier models by using asymptotic states.

Contribution

It introduces a method using asymptotic states to obtain physically meaningful photon spectra free from UV divergences during chiral mass shifts.

Findings

Photon spectra are UV finite with the new approach.

Mass shifts contribute significantly to photon production.

Method improves physical consistency of photon emission calculations.

Abstract

We investigate the photon emission arising from the shift of the quark/antiquark masses during the chiral phase transition in the early stage of ultrarelativistic heavy-ion collisions. As this mass shift leads to spontaneous creation of quark-antiquark pairs and thus contributes to the formation of the quark-gluon plasma, our investigations are relevant in the context of finite-lifetime effects on the photon emission from the latter. Earlier investigations on this topic by Boyanovsky et al. were plagued by a UV divergent contribution from the vacuum polarization and the non-integrability of the remaining contributions in the ultraviolet domain. In contrast to these investigations, we do not consider the photon number-density at finite times but for free asymptotic states obtained by an adiabatic switching of the electromagnetic interaction according to the Gell-Mann and Low theorem. This approach eliminates possible unphysical contributions from the vacuum polarization and renders the resulting photon spectra integrable in the ultraviolet domain. It is emphasized that the consideration of free asymptotic states is indeed crucial to obtain such physically reasonable results.