Quarkonium spectral function in medium at next-to-leading order for any quark mass

TL;DR

This paper calculates the vector channel spectral function in thermal QCD at next-to-leading order for any quark mass, revealing a well-defined transport peak and connecting to lattice results.

Contribution

It provides a comprehensive next-to-leading order calculation of the spectral function for arbitrary quark masses, including the massless limit, with implications for understanding quarkonium behavior in medium.

Findings

Transport peak is well-defined at NLO for any quark mass.

Massless limit can be taken without divergences.

Results are compared with lattice simulations.

Abstract

The vector channel spectral function at zero spatial momentum is calculated at next-to-leading order in thermal QCD for any quark mass. It corresponds to the imaginary part of the massive quark contribution to the photon polarization tensor. The spectrum shows a well defined transport peak in contrast to both the heavy quark limit studied previously, where the low frequency domain is exponentially suppressed at this order and the naive massless case where it vanishes at leading order and diverges at next-to-leading order. From our general expressions, the massless limit can be taken and we show that no divergences occur if done carefully. Finally, we compare the massless limit to results from lattice simulations.