Decaying neutrinos: The long way to isotropy

We investigate a scenario in which neutrinos are coupled to a pseudoscalar degree of freedom \(\ph\) and where decays \(\nu_1 \to \nu_2+\ph\) and inverse decays are the responsible mechanism for obtaining equilibrium. In this context we discuss the implication of the invisible neutrino decay on the neutrino-pseudoscalar coupling constant and the neutrino lifetime. Assuming the realistic scenario of a thermal background of neutrinos and pseudoscalar we update the bound on the (off-diagonal) neutrino-pseudoscalar coupling constant to \(g