Speaker
Dr
Jose R. Pelaez
(Universidad Complutense)
Description
The leading $1/N_c$ behaviour of Unitarised Chiral Perturbation Theory distinguishes the nature of the $\rho$ and the $\sigma$. At one loop order the $\rho$ is a ${\bar q}q$ meson, while the $\sigma$ is not. However, semi-local duality between resonances and Regge behaviour cannot be satisfied for larger $N_c$, if such a distinction holds. While the $\sigma$ at $N_c=3$ is inevitably dominated by its di-pion component, Unitarised Chiral Perturbation Theory beyond one loop order reveals that as $N_c$ increases above 6-8, the $\sigma$ has a sub-dominant ${\bar q}q$ fraction up at 1.2 GeV. Remarkably this ensures semi-local duality is fulfilled for the range of $N_c \lesssim 15$, where the unitarisation procedure adopted applies.
Primary author
Dr
Jose R. Pelaez
(Universidad Complutense)
Co-authors
Dr
David J. Wilson
(Thomas Jefferson National Accelerator Facility)
Mr
Jacobo Ruiz de Elvira
(Uni versidad Complutense de Madrid)
Prof.
Michael J. Pennington
(Thomas Jefferson National Accelerator Facility)
