Seesaw, coherence and neutrino oscillations

We present a prescription for consistently constructing non-Fock coherent flavour neutrino states within the framework of the seesaw mechanism, and establish that the physical vacuum of massive neutrinos is a condensate of Standard Model massless neutrino states. The coherent states, involving a finite number of massive states, are derived by constructing their creation operator. This construction fulfills automatically the key requirement of coherence for the oscillations of particles to occur. We comment on the inherent non-unitarity of the oscillation probability induced by the requirement of coherence.

Discussion on Lorentz invariance violation of noncommutative field theory and neutrino oscillation

Depending on deformed canonical anticommutation relations, massless neutrino oscillation based on Lorentz invariance violation in noncommutative field theory is discussed. It is found that the previous studies about massless neutrino oscillation within deformed canonical anticommutation relations should satisfy the condition of new Moyal product and new nonstandard commutation relations. Furthermore, comparing the Lorentz invariant violation parameters A in the previous studies with new Moyal product and new nonstandard commutation relations, we find that the orders of magnitude of noncommutative parameters (Lorentz invariant violation parameters A) is not self-consistent. This inconsistency means that the previous studies of Lorentz invariance violation in noncommutative field theory may not naturally explain massless neutrino oscillation. In other words, it should be impossible to explain neutrino oscillation by Lorentz invariance violation in noncommutative field theory. This conclusion is supported by the latest atmospheric neutrinos experimental results from the super-Kamiokande Collaboration, which show that no evidence of Lorentz invariance violation on atmospheric neutrinos was observed.

NEUTRINO MASSES AND LEPTOGENESIS FROM EXTRA FERMIONS

Generation of the neutrino masses and leptogenesis (LG) in the standard model extended by the heavy Majorana fermions is considered. Classification of LG scenarios according to the new fermion mass spectra is given, where singlet–triplet LG is considered for the first time. The upper bound on the CP asymmetry relevant for LG with hierarchical heavy neutrinos (Davidson–Ibarra bound) is revised, and shown that in the case of one massless neutrino it essentially depends on the type of the light neutrino mass hierarchy. The resonant scenarios, which help to avoid the problem of extremely high reheating temperature in the early universe, are discussed. In particular, we present new simplified, generalized and detailed formulation of freed LG, which violates Davidson–Ibarra bound in a special class of models.

LORENTZ VIOLATION IN THREE-FAMILY NEUTRINO OSCILLATION

We analyze the consequences of Lorentz violation (LV) to three-generation neutrino oscillation in the massless neutrino sector. We present a general formalism of three-family neutrino oscillation with neutrino flavor states being mixing states of energy eigenstates. It is also found that the mixing parts could strongly depend on neutrino energy by special choices of LV parameters. By confronting with the existing experimental data on neutrino oscillation, the upper bounds on LV parameters are derived. Because the oscillation amplitude could vary with the neutrino energy, neutrino experiments with energy dependence may test and constrain the LV scenario for neutrino oscillation.