What Can We Learn from Three-pion Interferometry?

We discuss the generalization of intensity interferometry from the case of two-particle correlations to three-particle correlations. We address the question whether three-particle Bose-Einstein correlations contain additional information on the shape and dynamics of the source which cannot be extracted from two-particle correlations. For chaotic sources we find that the true three-particle correlation term is sensitive to the momentum dependence of the saddle point of the source and to its asymmetries around that point, but that it will be experimentally very difficult to extract this information quantitively. For partially coherent sources the three-pion correlator allows to measure the degree of coherence without contamination from resonance decays.