Fast decaying neutrinos and observable flavour violation in a new class of majoron models

Abstract

Neutrinos can have any mass (allowed by laboratory limits) without violating limits from cosmology, astrophysics or laboratory searches for lepton violation phenomena. We present a simple extension of the standard theory where neutrinos decay dominantly into invisible modes involving a majoron associated with the spontaneous violation of B- L symmetry due to physics at or below the electroweak scale. Measurable branchings for lepton-flavour-violating processes such as μ→e+ γ, and for non-standard Z decays e.g. Z→ e+ τ , and Z→μ+ τ (plus their conjugates) at LEP are possible without unnatural fine-tuning of the parameters. Lepton-number-violating effects such as neutrinoless ββ decay may also be present at a measurable level.