Spin-dependent resonances in the conduction edge of quantum wires

The conductance through a quantum wire of cylindrical cross section and a weak bulge is determined exactly for two electrons within the Landauer-B\"uttiker formalism. We show that this ``open'' quantum dot exhibits spin-dependent resonances resulting in two anomalous structure on the rising edge to the first conductance plateau, one near ${0.25(2e}^{2}/h),$ related to a singlet resonance, and one near ${0.7(2e}^{2}/h),$ related to a triplet resonance. These resonances are generic and robust, occurring for other types of quantum wires and surviving to temperatures of a few degrees.