Aspects of baryon number as a U(1) symmetry.

The non-observation of proton decay strongly suggests that baryon number is a global U(1) (phase rotation) symmetry of the low-energy effective Lagrangian of particle physics. In the first half of this thesis, we explore the surprisingly dramatic consequences of this U(1) symmetry for the Affleck-Dine model of baryogenesis. Affleck-Dine baryogenesis is a popular model for the creation of a matter-antimatter asymmetry which relys on setting a complex scalar field into phase rotation. The phase symmetry of the Lagrangian has all important effect oil the evolution of this scalar field. The baryon number symmetry need not be restricted to a global symmetry. There is growing evidence from string theory, in fact, that global U(1) symmetries must have a gauge origin. In the second half of this thesis, we consider the details of how two different approaches to breaking a, gauged U(1) baryon symmetry would function in a universe with a low Planck scale. A universe with a low Planck scale (Mpl ∼ 103 GeV) has recently been shown to solve the long standing hierarchy problem of particle physics. In the absence of a gauged baryon symmetry the stability of the proton is thought to forbid a low Planck scale, yielding the limit Mpl > 1016 GeV. A gauged baryon symmetry can relax this restriction, but gauging baryon number presents many technical difficulties which must be addressed.PhDHigh energy physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125186/2/3186726.pd