Sigma-resonance and convergence of chiral perturbation theory

D. J. Cecile, Shailesh Chandrasekharan

The dimensionless parameter ${\xi }^{\prime }=M^2/(16{\pi }^2{F}^2)$, where $F$ is the pion decay constant in the chiral limit and $M$ is the pion mass at leading order in the quark mass, is expect…