  One-loop unitarized Chiral Perturbation Theory (UChPT) calculations, suggest
a different Nc behaviour for the sigma or f_0(600) and rho(770) mesons: while
the rho meson becomes narrower with Nc, as is expected for a q-qbar meson, the
sigma becomes broader, and its contribution to the total cross section is less
and less important. On the other hand, local duality requires a cancellation
between the sigma and rho amplitudes, but if there is a different Nc behaviour
for them, there is a possible contradiction between the Inverse Amplitude
Method (IAM) and local duality for large Nc. However, next to next to leading
order UChPT calculations suggested a subdominant q-qbar component for the sigma
with a mass around 1.2 GeV. In this work, we show that this subdominant q-qbar
component is indeed needed to ensure local duality.

High Energy Physics - Phenomenology