Citation
Erwin, Rebecca Joan (2007) Neutrino mass constraints on electroweak parameters. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd05252007084814
Abstract
We use the scale of neutrino mass and naturalness considerations to obtain modelindependent expectations for the magnitude of possible contributions to muon decay Michel parameters from new physics above the electroweak symmetrybreaking scale. Focusing on 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 and that contribute to both muon decay and neutrino mass. We show that  in the absence of fine tuning  the most stringent neutrino mass naturalness bounds on chiralitychanging vector operators relevant to muon decay arise from oneloop operator mixing. The bounds we obtain on their contributions to the Michel parameters are two orders of magnitude stronger than bounds previously obtained in the literature. In addition, we analyze the implications of oneloop matching considerations and find that the expectations for the size of various scalar and tensor contributions to the Michel parameters are considerably smaller than those derived from previous estimates of twoloop operator mixing. We also show, however, that there exist gaugeinvariant operators that generate scalar and tensor contributions 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.
We then repeat the analysis with Majorana neutrinos. Since the lowest dimension mass operator in this case is a fivedimensional operator, we start with a new basis of effective dimension five and dimension seven operators that contribute to muon decay and neutrino mass through radiative corrections. In contrast to similar studies of magnetic moments and masses using Dirac and Majorana neutrinos, which found substantially weaker bounds for Majorana magnetic moments, we find that the limits on muon decay Michel parameters from Majorana neutrinos are similar in magnitude to the limits from Dirac neutrinos. We also find, similar to the Dirac case, that there are operators in our basis whose coefficients are not bound by neutrino mass.
Finally, we calculate oneloop renormalization factors of twisttwo operators in massless QCD with domainwall fermions. The Shamir type domainwall fermion, with an infinitely large extra dimension to describe the massless fermion, is used.
Item Type:  Thesis (Dissertation (Ph.D.)) 

Subject Keywords:  domainwall fermions; muon decay; neutrino mass 
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:  24 May 2007 
Record Number:  CaltechETD:etd05252007084814 
Persistent URL:  http://resolver.caltech.edu/CaltechETD:etd05252007084814 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  2068 
Collection:  CaltechTHESIS 
Deposited By:  Imported from ETDdb 
Deposited On:  31 May 2007 
Last Modified:  26 Dec 2012 02:46 
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