Abstract:
Neutrino physics has been an active and successful research
field in recent years, especially experimentally. As a result of a
series of great experimental discoveries neutrino oscillations are
today a well established phenomenon indicating non vanishing
neutrino masses. If all the existing evidences of oscillation, coming
from the atmospheric and the solar neutrino experiments and the
laboratory experiment LSND, are described jointly, at least four
neutrino flavors are needed. The fourth flavor must be sterile with
respect to the Standard Model interactions since experiments show
that only three neutrino flavors couple to the Z-boson and we
discuss oscillations of atmospheric and solar neutrinos into sterile
neutrinos in the 2+2 scheme. To invalidate the 2+2 model, a global
fit to data with the small mixing angles included seems to be
required.
In this thesis various phenomenological aspects of sterile
neutrinos have been investigated. The lightness of the sterile
neutrino, required by the oscillation data, is a challenging problem
for theoretical model building.
In this thesis some of the most important present and future
neutrino experiments are described.It is shown that neutrino
oscillations can exist if the neutrino has mass and mixes. We derive
analytic expressions for three flavor neutrino oscillations in the
presence of matter in the plane wave approximation using the
Cayley Hamilton formalism. Especially, we calculate the time
evolution operator in both flavor and mass bases. Furthermore, we
find the transition probabilities, matter mass squared differences,
and matter mixing angles all expressed in terms of the vacuum
mass squared differences, the vacuum mixing angles, and the
matter density. The conditions for resonance in the presence of
matter are also studied in some examples.
