#### Date of Award

2014

#### Document Type

Dissertation

#### Degree Name

M.S. in Engineering Science

#### First Advisor

Alakabha Datta

#### Second Advisor

Ahmed Kishk

#### Third Advisor

Don Summers

#### Abstract

This work presents a study of the effects of multi-Higgs doublets on the properties of neutrino sector and heavy quark systems. The phenomenological implications of multi-Higgs models, which contain multi-Higgs doublets, in the neutrino and quark sector are discussed in this dissertation. The two-Higgs-doublet model (2HDM), in which two Higgs doublets are introduced, is the simplest extension to the scalar sector of the standard model (SM). A new boson state was recently seen in the CMS (Compact Muon Solenoid) and ATLAS (A Toroidal LHC Apparatus) experiments at the LHC (Large Hadron Collider). We investigate the multi-Higgs models contributions in understanding various phenomena in the neutrino sector. Introducing a model to explain the neutrino oscillation phenomenon within the framework of multi-Higgs doublets is considered. We introduce different flavor symmetries in the lepton sector and study the phenomenological consequences in both the scalar and lepton sectors. The leptonic mixing in the symmetric limit can be, among other structures, the bi-maximal (BM) or the tri-bimaximal (TBM) mixing. We find that a mixing model with 2-3 flavor symmetry can explain the nonzero θ13 measurements. In our study, neutrino masses were proposed where its smallness is not due to the seesaw mechanism, i.e. not inversely proportional to some large mass scale. It comes from a one-loop mechanism with dark matter in the loop consisting of singlet Majorana fermions within a model with A4 flavor symmetry. A relevant point of interest in the neutrino sector is the study of the nonstandered interactions and its implications to neutrino oscillation. Here, we introduce the nonstandard interaction effects at the detectors of neutrino oscillation experiments and the impact of extracting the neutrino mixing angles is studied. The extractions of the atmospheric mixing angle θ23 rely on the standard model cross sections for ντ + N → τ- + X in ν τ appearance experiments. Corrections to the cross sections from the charged Higgs and W’ contributions modify the measured mixing angle. We include form factor effects in the new physics calculations and find the deviations of the mixing angle. The quark sector has enriched our knowledge of particle physics. Lots of new theories and discovering new attributes of particles have been done in the quark sector. Therefore, we study the decay channel of the quarkonium η b → τ+ τ– to search for the existance of an additional Higgs field or a new gauge boson. We estimate the standard model branching ratio for this decay to be ∼ 4 × 10 –9. We show that considerably larger branching ratios, up to the present experimental limit of ∼ 8 percent, is possible in models with a light pseudoscalar or a light axial vector state. Also, in this dissertation we study the forward-backward asymmetry AFB in the top quark pair production in the t t¯ rest frame. In this work we seek for a new gauge boson to accommodating the CDF (Collider Detector at Fermilab) measurement of the AFB, which has a deviation from the next-to leading order (NLO) SM prediction. A u → t transition via a flavor-changing Z’ can explain the data. We consider the most general form of the tuZ’ interaction, which includes vector-axial vector as well as tensor type couplings, and study how these couplings affect the top forward-backward asymmetry.

#### Recommended Citation

Rashed, Ahmed, "Higgs Effects in Neutrino Physics and Heavy Quark Systems" (2014). *Electronic Theses and Dissertations*. 26.

https://egrove.olemiss.edu/etd/26

#### Concentration/Emphasis

Emphasis: Electrical Engineering