# Structure of virtual photon polarization in ultrarelativistic heavy-ion collisions

## TL;DR

This paper develops a theoretical framework to describe the polarization of virtual photons in anisotropic quark-gluon plasma created in ultrarelativistic heavy-ion collisions, linking polarization to collision anisotropy stages.

## Contribution

It introduces a generalized polarization operator structure for virtual photons in anisotropic media, including a new spectral function for asymmetric collision effects.

## Key findings

- Derived the general form of the photon polarization operator in anisotropic media.
- Connected polarization spectral functions to dilepton production rates.
- Identified a new spectral function reflecting collision asymmetry.

## Abstract

Anisotropy in heavy-ion collisions leads to polarization of both direct and virtual photons, the latter detected via internal conversion to dileptons pairs. Thus measurement of photon polarization probes the anisotropy at all stages of collisions. In order to characterize the polarization of virtual photons, we derive here the general structure of the photon polarization operator, rho^(mu nu), in an anisotropic medium, in terms of the four spectral functions, two transverse and one longitudinal, as usual, plus a new spectral function that reflects anisotropy in asymmetric collisions; and derive the local production rate of dilepton pairs in terms of these four functions.