Is Zee Model The Model of Neutrino Masses?

Abstract

Zee model leads naturally to two heavy, strongly degenerate and almost maximally mixed neutrinos and to one light neutrino with small mixing. This pattern coincides with the one needed for a solution of the atmospheric neutrino problem by $\n_\m\A \n_τ$ oscillations and for existence of the two component hot dark matter in the Universe. Furthermore, the oscillations $\bar\n_\m\A \bar\n_e$ can be in the range of sensitivity of KARMEN, LSND experiments. Phenomenology of this scenario is considered and possibility to check it in the forthcoming experiments is discussed. Scenario implies large values and inverse flavour hierarchy of the couplings of the Zee boson with fermions: $f_{e τ} \ll f_{μτ} \leq f_{e μ} \sim 0.1$. Main signatures of scenario are: strongly suppressed signal of $\n_\m\A \n_τ$ oscillation in CHORUS and NOMAD experiments, so that positive result from these experiments will rule out the scenario; possibility of observation of $\n_e\A \n_τ$ oscillations by CHORUS and NOMAD; corrections to the muon decay, neutrino-electron scattering at the level of the experimental errors; branching ratio $B(μ\A e γ)$ bigger than $10^{-13}$. The solar neutrino problem can be solved by introduction of additional very light singlet fermion without appreciable changes of the active neutrino pattern.