Theory of Soft Electromagnetic Emission in Heavy-Ion Collisions

TL;DR

This paper reviews how soft electromagnetic radiation, like thermal photons and dileptons, can diagnose the properties of strongly interacting matter created in ultrarelativistic heavy-ion collisions, linking spectral functions to fundamental QCD phenomena.

Contribution

It provides a comprehensive overview of electromagnetic emission rates from hadronic and quark-gluon plasma phases, incorporating recent lattice QCD insights and emphasizing their diagnostic potential.

Findings

Electromagnetic spectra serve as precise probes of QCD phase transitions.

Recent lattice QCD calculations enhance understanding of emission rates.

Electromagnetic signals can diagnose chiral symmetry restoration.

Abstract

A status report of utilizing soft electromagnetic radiation (aka thermal photons and dileptons) in the diagnosis of strongly interacting matter in ultrarelativistic heavy-ion collisions is given. After briefly elaborating on relations of the electromagnetic spectral function to chiral symmetry restoration and the transition from hadron to quark degrees of freedom, various calculations of electromagnetic emission rates in the hadronic and quark-gluon plasma phases of QCD matter are discussed. This, in particular, includes insights from recent thermal lattice QCD computations. Applications to dilepton and photon spectra in heavy-ion collisions highlight their role as a spectro-, thermo-, baro- and chrono-meter of extraordinary precision.