Coherent states in high-energy physics

The amplitude for emitting n bosons factorises into the product of n single-boson emission amplitudes, if the source is energetic and abelian. If it is energetic but non-abelian, the amplitude is given by a sum of factorized quasi-particle amplitudes. A quasi-particle is made up of an arbitrary number of bosons, but couples to the source like a single one. Factorization is related to coherence, and it allows computation of subleading contributions not obtainable by usual means. Its importance is illustrated in two applications: to solve the baryon problem in large-Nc QCD, and to obtain a total cross section satisfying the Froissart bound