Naturalness and Supersymmetry

TL;DR

This paper discusses the naturalness issues in supersymmetric models, highlighting the fine-tuning problems and proposing a gauge mediation model with a non-minimal messenger sector that alleviates some of these issues.

Contribution

It introduces a low-energy gauge mediation model with a non-minimal messenger sector that reduces fine tuning and is compatible with Grand Unified Theories.

Findings

Gauge mediation and heavy first-two-generation scalars reintroduce fine tuning.

Proposed non-minimal messenger sector improves Higgs mass generation.

Model remains consistent with Grand Unified Theories.

Abstract

Supersymmetry solves the gauge hierarchy problem of the Standard Model if the masses of supersymmetric partners of the SM particles are close to the weak scale. In this thesis, we argue 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. We study some of the constraints from the latter in this thesis. We have 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. We show 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. We also construct 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. We show that this model can be derived from a Grand Unified Theory despite the non-minimal spectrum.