Structure of the sigma meson and the softening

TL;DR

This paper investigates the internal structure of the sigma meson during chiral symmetry restoration, revealing different softening behaviors depending on whether it is a chiral partner or a dynamically generated resonance.

Contribution

It introduces dynamical chiral models to distinguish the sigma meson's structure as either a chiral partner or a dynamically generated resonance, analyzing their softening patterns.

Findings

Dynamically generated sigma meson softens differently from the chiral partner.

In symmetry restoration, both models show similar sigma meson behavior.

Softening patterns reflect the internal structure of the sigma meson.

Abstract

We study the structure of the sigma meson, the lowest-lying resonance of the pi pi scattering in the scalar-isoscalar channel, through the softening phenomena associated with the partial restoration of chiral symmetry. We build dynamical chiral models to describe the pi pi scattering amplitude, in which the sigma meson is described either as the chiral partner of the pion or as the dynamically generated resonance through the pi pi attraction. It is shown that the internal structure is reflected in the softening phenomena; the softening pattern of the dynamically generated sigma meson is qualitatively different from the behavior of the chiral partner of the pion. On the other hand, in the symmetry restoration limit, the dynamically generated sigma meson behaves similarly to the chiral partner.