Naturalness and supersymmetry

Abstract

In this thesis, the author argues that the supersymmetric Standard Model, while avoiding the fine tuning in electroweak symmetry breaking, requires unnaturalness/fine tuning in some (other) sector of the theory. For example, Baryon and Lepton number violating operators are allowed which lead to proton decay and flavor changing neutral currents. He studies some of the constraints from the latter in this thesis. He has to impose an R-parity for the theory to be both natural and viable. In the absence of flavor symmetries, the supersymmetry breaking masses for the squarks and sleptons lead to too large flavor changing neutral currents. He shows that two of the solutions to this problem, gauge mediation of supersymmetry breaking and making the scalars of the first two generations heavier than a few TeV, reintroduce fine tuning in electroweak symmetry breaking. He also constructs a model of low energy gauge mediation with a non-minimal messenger sector which improves the fine tuning and also generates required Higgs mass terms. He shows that this model can be derived from a Grand Unified Theory despite the non-minimal spectrum.