Chiral perturbation theory, the 1/N_c expansion and Regge behavior determine the structure of the lightest scalar meson

Abstract

The leading 1=N_c behavior of unitarized chiral perturbation theory distinguishes the nature of the ρ and the : The is a qq̅ meson, while the σ is not. However, semilocal duality between resonances and Regge behavior cannot be satisfied for larger N_c, if such a distinction holds. While the σ at N_c = 3 is inevitably dominated by its di-pion component, unitarized chiral perturbation theory also suggests that as N_c increases above 6–8, the σ may have a subdominant qq̅ fraction up at 1.2 GeV. Remarkably this ensures semilocal duality is fulfilled for the range of Nc ≤ 15–30, where the unitarization procedure adopted applies.