Classical Nambu-Goldstone fields

It is shown that a Nambu-Goldstone (NG) field may be coherently produced by a large number of particles in spite of the fact that the NG bosons do not couple to flavor conserving scalar densities such as ψ̅ ψ. If a flavor oscillation process takes place, the phases of the pseudoscalar or flavor-violating densities of different particles do not necessarily cancel each other. The NG boson gets a macroscopic source whenever the total (spontaneously broken) quantum number carried by the source particles suffers a net increase or decrease in time. If the lepton numbers are spontaneously broken such classical NG (Majoron) fields may significantly change the neutrino oscillation processes in stars, pushing the observational capabilities of neutrino-Majoron couplings down to m_ν/300 GeV.