The pion quasiparticle in the low-temperature phase of QCD

TL;DR

This study explores how the pion quasiparticle's properties change at low temperatures in QCD, revealing a reduced mass and consistent dispersion relations through lattice simulations and effective theory analysis.

Contribution

It provides the first lattice evidence that the pion quasiparticle mass decreases at low temperatures, contrasting with the static screening mass, and confirms the dispersion relation with multiple analysis methods.

Findings

Pion quasiparticle mass is significantly reduced at low temperature.

The dispersion relation and residue are consistent with theoretical predictions.

Results are confirmed by two independent analysis methods.

Abstract

We investigate the properties of the pion quasiparticle in the low-temperature phase of two-flavor QCD on the lattice with support from chiral effective theory. We find that the pion quasiparticle mass is significantly reduced compared to its value in the vacuum, in contrast to the static screening mass, which increases with temperature. By a simple argument, the two masses are expected to determine the quasiparticle dispersion relation near the chiral limit. Analyzing two-point functions of the axial charge density at non-vanishing spatial momentum, we find that the predicted dispersion relation and the residue of the pion pole are simultaneously consistent with the lattice data at low momentum. The test, based on fits to the correlation functions, is confirmed by a second analysis using the Backus-Gilbert method.