Majoron decay of neutrinos in matter.

Abstract

Using an helicity formalism for Majorana neutrino fields, we calculate the decay rates for the helicity-flipping and helicity-conserving Majoron decays of neutrinos propagating in dense media. We discuss the subtlety involved in the neutrino mixing in matter in a quantum-field-theoretical approach to clarify previous misunderstandings in the calculation of Majoron decays. General formulas, derived in a model-independent approach, can be applied to any number of neutrino generations and to the decay with production of any massless pseudoscalar boson. In particular, we discuss the two-generation case and show that in matter the helicity-flipping decays are dominant over the helicity-conserving decays. The implications of the Majoron decay for the neutrinos from astrophysical objects are also briefly discussed.