arXiv subjects
Publications and source records attributed to Nicole F. Bell.
We consider neutrino oscillations in a medium in which scattering processes are blind to the neutrino flavour. We present an analytical derivation of the synchronised behaviour obtained in the limit where the average scattering rate is much larger than the oscillation frequency. We also examine MSW transitions in these circumstances, and show that a sharpening of the transition can result.
We construct a model which provides maximal mixing between a pseudo-Dirac $ν_μ/ν_τ$ pair, based on a local $U(1)_{L_μ-L_τ}$ symmetry. Its strengths, weaknesses and phenomenological consequences are examined. The mass gap necessitated by the pseudo-Dirac structure is most naturally associated with the LSND anomaly. The solar neutrino problem then requires a light mirror or sterile neutrino. By paying a fine-tuning price to nullify the mass gap, one can also invoke $ν_e \to ν_{μ,τ}$ for the solar problem. The model predicts a new intermediate range force mediated by the light gauge boson of $U(1)_{L_μ-L_τ}$. Through the mixing of $μ$, $τ$ and $e$, this force couples to electrons and thus may be searched for in precision ``gravity'' experiments.
We investigate the mixing of heavy gauge singlet neutrinos in a mirror matter model employing the seesaw mechanism. The parameter constraints that must be satisfied to prevent the overproduction of mirror matter in the early universe are deduced. We find that no fine tuning in the heavy neutral fermion sector is required for this mirror matter model to satisfy cosmological constraints. Baryogenesis scenarios are briefly discussed in the context of the mirror model.
The exact Quantum Kinetic Equations for a two-flavour active-sterile neutrino system are used to provide a systematic derivation of approximate evolution equations for the relic neutrino asymmetry. An extension of the adiabatic approximation for matter-affected neutrino oscillations is developed which incorporates decoherence due to collisions. Exact and approximate expressions for the decoherence and repopulation functions are discussed. A first pass is made over the exact treatment of multi-flavour partially incoherent oscillations.
A consequence of the evaporation of primordial black holes in the early universe may be the generation of mirror matter. This would have implications with regard to dark matter, and the number of light particle species in equilibrium at the time of big bang nucleosynthesis. The possibilities for the production of mirror matter by this mechanism are explored.