Topics in neutrino oscillations, phenomenology of non-commutative field theories and CPT violation

In the first part of this thesis we study several scenarios for future long baseline neutrino oscillation experiments.; An approximation that is often used in fits to reactor and atmospheric neutrino data and in some studies of future neutrino oscillation experiments is to assume one dominant mass scale. We investigate the corrections to this approximation arising from the second mass scale, assuming the large mixing angle solution to the solar neutrino problem. We show that, in the range of interest for long-baseline neutrino oscillation experiments, the contributions to $nm\to ne$ oscillations from terms involving solar parameters can be comparable to the contributions involving the terms with the dominant mass scale. We also consider generalized analyzes of reactor and atmospheric neutrino data and present calculations of matter effects in a three-flavors, two mass scales framework relevant to this data and to neutrino factory measurements.; We also study the capabilities of a low energy, long baseline neutrino oscillation experiment.; The second part of the thesis addresses the phenomenology of non-commutative field theories. The presence of the non-commutativity parameter $qmn$, a constant antisymmetric tensor of dimension (−2), leads to the violation of Lorentz invariance.; We assume that the zeroth order term in $q$-expansion represents the Standard Model and study the effects induced by linear terms in $qmn$. If the coupling to $qmn$ is realized in the strongly interacting sector of the theory, clock comparison experiments place the limit on the possible size of this background at the level of $1q\gtrsim$ 5 × 1014 GeV. If the interaction with $qmn$ is initially present only in the QED sector, this limit can be relaxed to 1011–1012 GeV. We also show that, in certain models, mixed non-commutativity leads to CPT violation in four dimensions.; The third part of the thesis discusses CPT violation in the leptonic sector. CPT violation in the neutrino sector, suggested as a new way to reconcile different neutrino anomalies, induces at the radiative level observable effects among charged leptons, where high-precision tests of the CPT symmetry are available. We show that, in models with heavy right-handed Majorana neutrinos, constraints imposed by these experiments require CPT violation in neutrino spectrum be suppressed to a level undetectable for any conceivable neutrino experiment. We find that CPT violation in the neutrino sector may evade indirect constraints only at the expense of light right-handed neutrinos with small Yukawa couplings to the Standard Model sector or by allowing non-locality well below the electroweak scale. (Abstract shortened by UMI.)...