Bright branes for strongly coupled plasmas

TL;DR

This work addresses non-perturbative photon production in strongly coupled, finite-temperature gauge theories with fundamental matter by leveraging gauge/gravity duality. Using D3/D7 and D4/D6 probe-brane constructions, the authors compute the electromagnetic current spectral function at light-like momenta and extract photon emission rates to leading order in the electromagnetic coupling while fully summing the gauge interactions. They obtain explicit results for massless quarks and perform numerical studies for massive quarks, uncovering how the spectral function and emission rate depend on frequency $\omega$ and quark mass via the dimensionless parameter $M_q/T$, including near-critical regimes where sharp resonances emerge. The findings reveal universal qualitative features across models, such as monotonic suppression with mass at low $\omega$, crossovers at intermediate frequencies, and model-dependent high-frequency falloffs; these insights have potential implications for interpreting photon signals in heavy-ion collisions and illustrate how holography encodes real-time plasma dynamics.

Abstract

We use holographic techniques to study photon production in a class of finite temperature, strongly coupled, large-Nc SU(Nc) quark-gluon plasmas with Nf << Nc quark flavours. Our results are valid to leading order in the electromagnetic coupling constant but non-perturbatively in the SU(Nc) interactions. The spectral function of electromagnetic currents and other related observables exhibit an interesting structure as a function of the photon frequency and the quark mass. We discuss possible implications for heavy ion collision experiments.