Citation
Wang, Peng (2007) Neutrino mass implications for physics beyond the Standard Model. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd05312007144931
Abstract
We begin by working out an effective field theory valid below some new physics scale for Dirac neutrinos and Majorana neutrinos, respectively. For Dirac neutrinos, we obtain a complete basis of effective dimension four and dimension six operators that are invariant under the gauge symmetry of the Standard Model. As for Majorana neutrinos, we come up with a complete basis of effective dimension five and dimension seven operators that are invariant under the gauge symmetry of the Standard Model. Using the effective theory, we derive modelindependent, "naturalness" upper bounds on the magnetic moments of Dirac neutrinos and Majorana neutrinos generated by physics above the scale of electroweak symmetry breaking. In the absence of finetuning of effective operator coefficients, for Dirac neutrinos, we find that current information on neutrino mass implies that the bound on neutrino magnetic moments is several orders of magnitude stronger than those obtained from analyses of solar and reactor neutrino data and astrophysical observations. As for Majorana neutrinos, the magnetic moment contribution to the mass is Yukawa suppressed. The bounds we derive for magnetic moments of Majorana neutrinos are weaker than present experimental limits if neutrino magnetic moments are generated by new physics at around 1 TeV, and surpass current experimental sensitivity only for new physics scales >10100 TeV. The discovery of a neutrino magnetic moment near present limits would thus signify that neutrinos are Majorana particles. Then, we use the scale of neutrino mass to derive modelindependent naturalness constraints on possible contributions to muon decay Michel parameters. We show that  in the absence of finetuning  the most stringent bounds on chiralitychanging operators relevant to muon decay arise from oneloop contributions to neutrino mass. The bounds we obtain on their contributions to the Michel parameters are four or more orders of magnitude stronger than bounds previously obtained in the literature. We also show that, if neutrinos are Dirac fermions, there exist chiralitychanging operators that contribute to muon decay but whose flavor structure allows them to evade neutrino mass naturalness bounds. We discuss the implications of our analysis for the interpretation of muon decay experiments. Finally, we use the upper limit on the neutrino mass to derive modelindependent naturalness constraints on some nonStandardModel interactions of beta decays. In the absence of finetuning of effective operator coefficients, our results yield constraints on scalar and tensor weak interactions one or more orders of magnitude stronger than a recent global fit after combined with the current experimental limits. We also show that, if neutrinos are Majorana fermions, there exist fourfermion operators that contribute to beta decay but whose flavor structure allows them to evade neutrino mass naturalness bounds. Constraints on the beta decay parameters by CKM Unitarity, ratio of positive pion decays, and pion beta decays are discussed as well.
Item Type:  Thesis (Dissertation (Ph.D.)) 

Subject Keywords:  beta decay; muon decay; Neutrino 
Degree Grantor:  California Institute of Technology 
Division:  Physics, Mathematics and Astronomy 
Major Option:  Physics 
Thesis Availability:  Public (worldwide access) 
Research Advisor(s): 

Thesis Committee: 

Defense Date:  23 May 2007 
Author Email:  pengw (AT) theory.caltech.edu 
Record Number:  CaltechETD:etd05312007144931 
Persistent URL:  http://resolver.caltech.edu/CaltechETD:etd05312007144931 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  2342 
Collection:  CaltechTHESIS 
Deposited By:  Imported from ETDdb 
Deposited On:  04 Jun 2007 
Last Modified:  26 Dec 2012 02:50 
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