Probing Dynamical Electrical Conductivity via Dilepton Emission: A Kinetic theory approach

TL;DR

This paper develops an analytical approach to calculate thermal dilepton spectra and elliptic flow from the Quark-Gluon Plasma using kinetic theory, revealing how relaxation time and magnetic fields influence observable signals.

Contribution

It introduces the first analytical expression for dilepton rates with explicit relaxation time dependence within relativistic kinetic theory.

Findings

Dilepton rate shows non-monotonic dependence on relaxation time.

Magnetic fields can modify spectra and flow by up to 20%.

Results are consistent with previous quantum field theory calculations.

Abstract

Dileptons serve as a clean and penetrating probe of the Quark--Gluon Plasma created in high-energy heavy-ion collisions. In this work, we investigate thermal dilepton spectra and their elliptic flow through the dynamical conductivity that governs the production rate. The conductivity is obtained from the trace of the spectral function within relativistic kinetic theory using the Relaxation Time Approximation. This allows us to derive for the first time an analytical expression for the dilepton rate with explicit dependence on the relaxation time of quark-antiquark interactions. We find a non-monotonic dependence of the dilepton rate on the relaxation time and compare the resulting transverse momentum, invariant mass spectra and elliptic flow with previous quantum field theory results. The spectra and elliptic flow are obtained by integrating the rate over the full spacetime volume of the evolving medium, using temperature and flow profiles from realistic MUSIC hydrodynamic simulations without considering the effect of magnetic fields in the profiles itself. However, we study the role of an external space-time dependent magnetic field by making the conductivity anisotropic. At small relaxation times, magnetic fields have negligible impact, while for larger relaxation times and stronger initial fields, modifications of up to $\sim$20\% appear in both spectra and elliptic flow. Assuming instead a constant magnetic field of $\sim 1\,m_{\pi}^2$ at large relaxation times yields more modest effects, with changes of about 10\% in spectra and 5\% in elliptic flow.