Prediction of Feshbach resonances in collisions of ultracold rubidium atoms

On the basis of recently measured Rb2 bound-state energies and continuum properties, we predict magnetically induced Feshbach resonances in collisions of ultracold rubidium atoms. The resonances make it possible to control the sign and magnitude of the effective particle-particle interaction in a Rb Bose-Einstein condensate by tuning a bias magnetic field. For the case of 85Rb they occur at field values in the range where these atoms can be magnetostatically trapped. For 87Rb they are predicted to occur at negative field values