Enhanced non-quark-antiquark and non-gluebal N_c behavior of light scalar mesons

TL;DR

This paper investigates the nature of light scalar mesons, showing that their properties do not align with simple quark-antiquark or glueball models unless unnatural fine tuning is assumed, unlike vector mesons.

Contribution

The study introduces a method using scattering observables to test 1/N_c predictions directly at N_c=3, challenging traditional interpretations of light scalar mesons.

Findings

Scalar mesons do not fit quark-antiquark or glueball models without fine tuning.

The method uses dispersive scattering data to evaluate 1/N_c predictions at physical N_c.

Results suggest alternative explanations for light scalar mesons beyond conventional models.

Abstract

We report our results on the nature of the lightest scalar resonances, where we show that a quark-antiquark or glueball interpretation of the scalars f_0(600) and K^*_0(800) requires a very unnatural fine tuning to satisfy 1/N_c-expansion predictions for quark-antiquark or glueball states, which is not needed in the case of the lightest vector mesons \rho(770) and K^*(892). For this we consider scattering observables whose value is fixed to 1 for quark-antiquark and glueball states up to corrections suppressed by more than one power of 1/N_c, thus enhancing contributions of other nature. This allows us to evaluate these observables and check the 1/N_c predictions at N_c=3 without the need to extrapolate to unphysical N_c values. This is done using recent and very precise dispersive \pi\pi and \pi K scattering data analyses.