Structure of Λ(1405) and Threshold Behavior of πΣ Scattering

The scattering length and effective range of the pi Sigma channel are studied in order to characterize the strangeness S = -1 meson-baryon scattering and the Lambda(1405) resonance. We examine various off-shell dependence of the amplitude in dynamical chiral models to evaluate the threshold quantities with the constraint at the (K) over barN threshold. We find that the pi Sigma threshold parameters are important to the structure of the Lambda(1405) resonance and provide further constraints on the subthreshold extrapolation of the (K) over barN interaction.