  In this thesis we investigate several topics in neutrino physics, with an em-
phasis on the phenomenology of the sterile neutrinos. We study the existence of
a light sterile neutrino within the so called 3+1 scenario using the data of
the medium baseline reactor experiments. We will also probe the parameters of
the Large Extra Dimension model with the high energy atmospheric data of the
IceCube experiment, and will find an equivalence between the Kaluza Klein modes
and the sterile neutrinos. We will study the secret interaction of the ster-
ile neutrinos which is proposed to solve the tension between cosmology and the
sterile neutrino hypothesis. In addition to these, we will show that a minimal
2-Higgs-Doublet-Model extended with a U(1) or Z_2 symmetry cannot explain the
smallness of the neutrino masses.
