Abstract
A sterile neutrino in the 3+1 scheme, where the sterile accounts for neutrino anomalies not explained solely by the weak active neutrinos, arises as a natural source for the breaking of the mu -tau symmetry suggested by oscillation neutrino data. We explore the predictions for the Dirac CP phases in this scenario, with and without sterile neutrino decay, and show that current limits on delta _{CP} suggest a normal hierarchy and a lightest neutrino scale below 0.1 eV as the most plausible explanation for that, when Majorana phases are null. Other Dirac phases turn out to be non zero as well.
Highlights
The Standard Model (SM) has proved to be a very precise theory to explain most phenomena regarding fundamental particles and their interactions, it is by no means a complete theory, in the sense that there are still some issues for which it has not a solution, at least not in its original form, i.e., as a quantum field theory with the gauge group SU (2)L × U (1)Y
A sterile neutrino in the 3 + 1 scheme, where the sterile accounts for neutrino anomalies not explained solely by the weak active neutrinos, arises as a natural source for the breaking of the μ − τ symmetry suggested by oscillation neutrino data
We have explored the parameter space of a 3 + 1 scheme for neutrino oscillations, where exact μ − τ symmetry is assumed to be valid in the active neutrino sector, but which is explicitly broken in the active-sterile neutrino mass matrix terms, searching for its predictions about Dirac like phases
Summary
The Standard Model (SM) has proved to be a very precise theory to explain most phenomena regarding fundamental particles and their interactions, it is by no means a complete theory, in the sense that there are still some issues for which it has not a solution, at least not in its original form, i.e., as a quantum field theory with the gauge group SU (2)L × U (1)Y. Though, do ignore data coming from LSND [32] and MiniBooNe [33,34] experiments, which have observed some events identified as the appearance above background of electron neutrinos (antineutrinos) within an originally muon neutrino (antineutrino) flux This observations are troublesome for the three standard neutrino scheme, since to explain such events within the picture of flavor oscillations, data implies a larger mass scale, about m2 ∼ 1 eV 2, with a rather small mixing angle, sin θL SN D ≈ 0.0023. Besides the preference for the normal hierarchy, which is hinted to from cosmology [53], we will see a significant difference for the allowed mass values reported in this work when compared with the results obtained in [28] Such distinction is due to the complex nature of the mass matrix elements in the sterile sector. An Appendix with a more detailed description of the diagonalization of the mass matrix has been added
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