#### Degree Type

Dissertation

#### Date of Award

2014

#### Degree Name

Doctor of Philosophy

#### Department

Physics and Astronomy

#### First Advisor

Kerry Whisnant

#### Abstract

In this thesis, we studied the phenomenological results of several classes of neutrino models. We begin with an investigation of the effect of small perturbations on the &mu-&tau symmetrical models. We found that since m_{1} and m_{2} are nearly degenerate, &mu-&tau symmetry mixing scenarios are able to explain the experimental data with about the same size perturbation for most values of &\theta_{12}. This suggests that the underlying unperturbed mixing need not have &\theta_{12} close to the experimentally preferred value.

Then we studied a simple case of type I seesaw model that have four texture zeros in the Yukawa couplings matrix, which is equivalent to a single texture or cofactor zero for an off-diagonal element of the light neutrino mass matrix *M* in the context of low energy phenomenology. Furthermore we studied a variety of neutrino models that have one or two texture and/or cofactor zeros. We determined the constraints in the space of the CP phase and lightest neutrino mass using a global fit to neutrino parameters, including recent data on &\theta_{13}. We used leptogenesis to further constrain the parameter space for the seesaw models with four zeros in the Yukawa matrix, and made predictions on neutrinoless double beta decay for these models.

Finally we showed that any neutrino model with a homogeneous relationship among elements of the light neutrino mass matrix with one mass hierarchy predicts oscillation parameters and Majorana phases similar to those of models with the same homogeneous relationship among cofactors of the mass matrix with the opposite mass hierarchy if the lightest mass is not too small, e.g., less than about 20 meV. This general result applies to texture and/or cofactor zero models, scaling models, and models that have two equal mass matrix elements or cofactors, e.g. &mu-&tau symmetric models.

#### Copyright Owner

Jiajun Liao

#### Copyright Date

2014

#### Language

en

#### File Format

application/pdf

#### File Size

116 pages

#### Recommended Citation

Liao, Jiajun, "Phenomenological studies of neutrino physics" (2014). *Graduate Theses and Dissertations*. 14224.

https://lib.dr.iastate.edu/etd/14224