How to understand the lightest scalars

TL;DR

This paper uses a coupled channel model to analyze light scalar mesons, revealing that certain resonances are different manifestations of the same quark state and explaining the nature of the sigma meson.

Contribution

It introduces a comprehensive coupled channel approach that accounts for multiple thresholds, unitarity, and analyticity to understand light scalar mesons and their resonance poles.

Findings

f0(980) and f0(1370) are two manifestations of the same strange-antistrange quark state

The sigma meson appears as a broad resonance with a pole at 470-i250 MeV

The model explains the nature of light scalar mesons through unitarization and hadronic mass shifts

Abstract

Based on previous papers I discuss how I understand the lightest scalars using a general coupled channel model. This model includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. One finds that with a large coupling there can appear two physical resonance poles on the second sheet although only one bare quark-antiquark state is put in. The f0(980) and f0(1370) resonance poles are thus in this model two manifestations of the same strange-antistrange quark state. On the other hand, the isoscalar state containing u and d quarks becomes (when unitarized and strongly distorted by hadronic mass shifts) a very broad resonance, with its pole at 470-i250 MeV. This is the sigma meson required by models for spontaneous breaking of chiral symmetry.