On the non-existence of resonances above the ionization threshold in positron-hydrogen scattering

The hyperspherical close-coupling method is applied to obtain both the elastic and positronium-formation cross sections for positron collisions with atomic hydrogen at energies above the ionization threshold for the J = 0 and J = 1 partial waves. In contrast to many previous results from the standard close-coupling calculations, no resonance structures were found in the present results and the cross sections were found to vary smoothly with collision energies. A possible explanation for the occurrence of ''resonances'' in previous calculations is also proposed. (Author)