First-order chiral phase transition may naturally lead to the ``quenched'' initial condition and strong soft-pion fields

TL;DR

The paper introduces a new mechanism for disoriented chiral condensate (DCC) formation during a first-order chiral phase transition, involving bubble nucleation and supercooling that amplify soft pion modes.

Contribution

It presents a novel scenario where a first-order transition traps the chiral field, leading to a quenched initial condition and enhanced soft pion production, which was not previously considered.

Findings

Bubble nucleation can trap the chiral field at zero, creating a quenched initial state.

Supercooling allows the bubble to overshoot and align with the vacuum, amplifying soft pions.

The mechanism may explain baryon rapidity fluctuations associated with DCCs.

Abstract

We propose a novel mechanism for DCC formation in a first-order chiral phase transition. In this case the effective potential for the chiral order parameter has a local minimum at $\Phi\sim 0$ in which the chiral field can be ``trapped''. If the expansion is sufficiently fast a bubble of disoriented chiral field can emerge and decouple from the rest of the fireball. The bubble may overshoot the mixed phase and subsequently supercool until the barrier disappears, when the potential resembles that at T=0. This situation corresponds to the initial condition realized in a ``quench''. Thus, the subsequent alignment in the vacuum direction leads to strong amplification of low momentum modes of the pion field. We propose that these DCCs could accompany the previously suggested baryon rapidity fluctuations.