Chiral Restoration in the Early Universe: Pion Halo in the Sky

TL;DR

This paper explores the nature of chiral symmetry restoration in the early universe, revealing that pions remain as Nambu-Goldstone particles at high temperatures due to spacelike cuts in the fermion propagator, challenging previous dissociation models.

Contribution

It introduces a spacetime quantization of the effective quark action showing that spacelike cuts lead to a thermal vacuum where pions do not dissociate at high temperatures.

Findings

Pions remain Nambu-Goldstone particles at high T.

The thermal vacuum is a generalized NJL state with a 90° phase.

Spacelike cuts influence chiral symmetry and pion behavior.

Abstract

< \psibarpsi > vanishing above $T_c$ indicates chiral symmetry restoration at high $T$. But is it the old $T=0$ chiral symmetry that is `restored'? In this talk, I report on the spacetime quantization of the BPFTW effective action for quarks in a hot environ. The fermion propagator is known to give a pseudo-Lorentz invariant particle pole as well as new spacelike cuts. Our quantization shows that the spacelike cuts directly lead to a thermal vacuum that is a generalized NJL state, with a curious $90^{o}$ phase. This $90^{o}$ is responsible for < \psibarpsi > vanishing at high $T$. The thermal vacuum is invariant under a new chiral charge, but continues to break the old zero temperature chirality. Our quantization suggests a new class of order parameters that probe the physics of these spacelike cuts. In usual scenario, the pion dissociates in the early alphabet soup. With this new understanding of the thermal vacuum, the pion remains a Nambu-Goldstone particle at high $T$, and will not dissociate. It propagates at the speed of light but with a halo.