The quark and lepton mass matrices possess approximate flavor symmetries. Several results follow if the interactions of new scalars possess these approximate symmetries. Present experimental bounds allow these exotic scalars to have a weak scale mass. The Glashow-Weinberg criterion is rendered unnecessary. Finally, rare leptonic B meson decays provide powerful probes of these scalars, especially if they are leptoquarks.
Stringent bounds on baryon and lepton number violating interactions have been derived from the requirement that such interactions, together with electroweak instantons, do not destroy a cosmological baryon asymmetry produced at an extremely high temperature in the big bang. While these bounds apply in specific models, we find that they are generically evaded. In particular, the only requirement for a theory to avoid these bounds is that it contain charged particles which, during a certain cosmological epoch, carry a non-zero hypercharge asymmetry. Hypercharge neutrality of the universe then dictates that the remaining particles must carry a compensating hypercharge density, which is necessarily shared amongst them so as to give a baryon asymmetry. Hence the generation of a hypercharge density in a sector of the theory forces the universe to have a baryon asymmetry. PACS number(s): 05.20. 98.80.Cq
Over the past couple of decades, the Standard Model of high energy particle physics has clearly established itself as an invaluable tool in the analysis of high energy particle phenomenon. However, from a field theorists point of view, there are many dissatisfying aspects to the model. One of these, is the large number of free parameters in the theory arising from the Yukawa couplings of the Higgs doublet.In this thesis, we examine various issues relating to the Yukawa coupling structure of high energy particle field theories. We begin by exam- M Aining extensions to the Standard Model of particle physics which contain additional scalar fields. By appealing to the flavor structure observed in the fermion mass and Kobayashi-Maskawa matrices, we propose a reasonable phenomenological parameterization of the new Yukawa couplings based on the concept of approximate flavor symmetries. It is shown that such a parameterization eliminates the need for discrete symmetries which limit the allowed couplings of the new scalars. New scalar particles which can mediate exotic flavor changing reactions can have masses as low as the weak scale.Next, we turn to the issue of neutrino mass matrices, where we examine a particular texture which leads to matter independent neutrino oscillation results for solar neutrinos. Using a nonstandard basis for our parameterization, we argue that such a mass matrix has a far larger allowed parameter space than the standard see-saw mass matrices. We propose a model which gives rise to such a matrix, finding that approximate flavor symmetries are an important tool in its construction. The experimental consequences of this model are discussed in detail.We, then, examine the basis for extremely strict limits placed on flavor changing interactions which also break lepton-and/or baryon-number. These limits are derived from cosmological considerations. Such interactions, when in equilibrium simultaneously with electroweak instantons, can destroy an existing asymmetry in baryon number. We find that it is a simple matter to avoid these limits entirely, and that one need not impose a symmetry which has a baryon number component in order to do so.Finally, we embark on an extended analysis of proton decay in supersymmetric SO( 10) grand unified theories. In such theories, the dominant decay diagrams involve the Yukawa couplings of a heavy triplet superfield. We argue that past calculations of proton decay which were based on the minimal supersymmetric SU(5) model require reexamination because the Yukawa couplings of that theory are known to be wrong. By analyzing the flavor structure of a class of SO(l0) theories which do not suffer form this problem , we determine that proton decay branching ratios and dominant diagrams can differ substantially from previous expectations. We discuss, in some generality, the circumstances in which charged lepton decay modes have large branching ratios and in which gluino diagrams DISCLAIMERPortions of this document may be iliegible in electronic image products. Ima...
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