Naturalness of electroweak physics within minimal supergravity

TL;DR

This paper evaluates the naturalness of electroweak physics within minimal supergravity, considering experimental constraints and fine tuning, and identifies the most natural parameter regions with implications for future detection.

Contribution

It provides a detailed quantitative analysis of fine tuning in minimal supergravity, incorporating the latest experimental data and dark matter constraints.

Findings

Minimum fine tuning is 1 part in 9 without dark matter constraints.

Minimum fine tuning is 1 part in 15 with dark matter constraints.

Natural regions favor light fermions and heavy scalars in the spectrum.

Abstract

Low energy supersymmetry is motivated by its use as a solution to the hierarchy problem of the electroweak scale. Having motivated this model with naturalness arguments, it is then necessary to check whether the experimentally allowed parameter space permits realisations of the model with low fine tuning. The scope of this thesis is a study of naturalness of the electroweak physics in the minimal supergravity model. The latest experimental constraints are applied, and the fine tuning is quantitatively evaluated for a scan across the parameter space. The fine tuning of the electroweak scale is evaluated at 2-loop order, and the fine tuning of the neutralino dark matter thermal relic energy density is also determined. The natural regions of the parameter space are identified and the associated phenomenology relevant for detection discussed. Naturalness limits are also found for the parameter space and spectrum. The minimum fine tuning found is 1 part in 9 when dark matter constraints are neglected, and 1 part in 15 when dark matter constraints are satisfied. For both cases, the minimum fine tuning is found for a Higgs mass of 115 GeV irrespective of whether the Higgs mass constraint is applied or not. The most natural spectrum includes light superpartner fermions, and heavy superpartner scalars. Minimal supergravity currently remains viable with respect to naturalness and a natural realisation may be discovered within the next couple of years.