The pion quasiparticle in the low-temperature phase of QCD

TL;DR

This study examines how the pion quasiparticle's properties change in the low-temperature phase of QCD, revealing a significant mass reduction and confirming the dispersion relation through lattice simulations and advanced analysis methods.

Contribution

It provides the first lattice QCD evidence that the pion quasiparticle mass decreases at low temperatures and validates the dispersion relation using multiple analysis techniques.

Findings

Pion quasiparticle mass is reduced compared to vacuum

Dispersion relation and residue are consistent with lattice data

Backus-Gilbert method confirms the results

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, by contrast with the static screening mass, which increases with temperature. By a simple argument, near the chiral limit the two masses are expected to determine the quasiparticle dispersion relation. 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.