BPS States with Extra Supersymmetry

A state saturating a BPS bound derived from a supersymmetry algebra preserves some fraction of the supersymmetry. This fraction of supersymmetry depends on the charges carried by the system, and we show that in general there are configurations of charges for which a BPS state would preserve more than half the original supersymmetry. We investigate configurations that could preserve 3/4 supersymmetry in string theory, M-theory and supersymmetric field theories and discuss whether states saturating these bounds actually occur in these theories.