Barry, James Munnik Hamilton (2009) Comparison of A₄ neutrino mass models. Masters thesis, Rhodes University.

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Abstract
The present neutrino oscillation data are compatible with tribimaximal mixing, to leading order. The addition of an A₄ family symmetry and extended Higgs sector to the Standard Model can generate this mixing pattern, assuming the correct vacuum expectation value alignment of Higgs scalars. The effect of deviating this alignment is studied, for different types of A₄ models, with a phenomenological emphasis: the effect of perturbations on the model predictions for the neutrino oscillation and neutrino mass observables. The standard theoretical description of neutrino oscillations is presented, along with a summary of the past, present and future experimental efforts aimed at measuring the neutrino mixing parameters. Additionally, the current constraints on the sum of absolute neutrino masses and the amplitude for neutrinoless double beta decay, which is yet to be observed, are discussed. These constraints provide a modelindependent test of family symmetery models. The Standard Model is reviewed, and extensions to the Standard Model such as the seesaw mechanism(s) are discussed: these are designed to endow neutrinos with mass, and can be incorporated into A₄ symmetry models. Models with different A₄ particle assignments are analysed for deviations from tribimaximal mixing. There are nine models presented in Chapter 5, with lepton doublets transforming as 3 and righthanded charged leptons transforming as 1, 1', 1"; five of these include righthanded neutrinos transforming as 3, and make use of the seesaw mechanism. Chapter 6 contains the analysis of six models that assign all leptons to the 3 representation, with four of these utilising the seesaw mechanism. The models are tested for any degree of fine tuning of the parameters that define the mass matrices. The effect of perturbations on the mixing angle observables, in particular sin² θ[subscript 13] and sin² θ[subscript 23], is studied, as well as the effect on the Jarlskog invariant, J[subscript CP] . Investigations of the <m[subscript ee]>  Σm[subscript v] parameter space allow for comparison with current data, and can lead to the possible exclusion of a particular model by constraints from future data.
Item Type:  Thesis (Masters) 

Uncontrolled Keywords:  Neutrinos  Mass, Standard model (Nuclear physics), Particles (Nuclear physics), flavour symmetry, trib.maximal mixing, A₄ 
Subjects:  Q Science > QC Physics 
Divisions:  Faculty > Faculty of Science > Physics & Electronics 
Supervisors:  Karataglidis, S (Prof) 
ID Code:  1790 
Deposited By:  Mrs Carol Perold 
Deposited On:  16 Feb 2011 13:24 
Last Modified:  06 Jan 2012 16:21 
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