Oscillations of the mixed pseudo--Dirac neutrinos

TL;DR

This paper investigates neutrino oscillations in a pseudo-Dirac framework, proposing a specific mass matrix structure that explains solar, atmospheric, and LSND neutrino oscillation phenomena, with potential for alternative interpretations.

Contribution

It introduces a novel neutrino mass matrix model with dominant off-diagonal entries, explaining multiple neutrino oscillation effects within a pseudo-Dirac neutrino scenario.

Findings

Neutrino oscillations can account for solar, atmospheric, and LSND anomalies.

Atmospheric neutrinos mainly oscillate into tau neutrinos.

Solar neutrinos oscillate into Majorana sterile neutrinos.

Abstract

Oscillations of three pseudo--Dirac flavor neutrinos $\nu_e, \nu_\mu, \nu_\tau$ are considered: $0 < m^{(L)} = m^{(R)} \ll m^{(D)}$ for their Majorana and Dirac masses taken as universal before family mixing. The actual neutrino mass matrix is assumed to be the tensor product $ M^{(\nu)} \otimes {(\begin{array}{cc} \lambda^{(L)} & 1 1 & \lambda^{(R)} \end{array})}$, where $M^{(\nu)}$ is a neutrino family mass matrix ($ M^{(\nu) \dagger} = M^{(\nu)}$) and $\lambda^{(L,R)} = m^{(L,R)}/m^{(D)}$. The $ M^{(\nu)}$ is tried in a form proposed previously for charged leptons $e, \mu, \tau$ for which it gives $m_\tau = 1776.80$ MeV versus $m^{exp}_\tau = 1777.05^{+0.29}_{-0.20}$ MeV (with the experimental values of $m_e$ and $m_\mu$ used as inputs). However, in contrast to the charged -lepton case, in the neutrino case its off-diagonal entries dominate over diagonal. Then, it is shown that three neutrino effects (the deficits of solar $\nu_e$'s and atmospheric $\nu_\mu$'s as well as the possible LSND excess of $\nu_e$'s in accelerator $\nu_\mu$ beam) can be explained by neutrino oscillations though, alternatively, the LSND effect may be eliminated (by a parameter choice). Atmospheric $\nu_\mu$'s oscillate dominantly into $\nu_\tau$'s, while solar $\nu_e$'s -- into (automatically existing) Majorana sterile counterparts of $\nu_e$'s.