Constraints on the mSUGRA parameter space from electroweak precision data

TL;DR

This paper investigates how electroweak precision data constrains the parameter space of the mSUGRA model, focusing on loop contributions of supersymmetric particles and their implications for collider phenomenology.

Contribution

It provides a detailed analysis of electroweak constraints on mSUGRA parameters, emphasizing the importance of propagator corrections and the (b ---> s gamma) process in certain regions.

Findings

Constraints are significant in the small-m_0 and small-m_{1/2} region.

The process (b ---> s gamma) enlarges the constrained region for mu < 0 and large tan(beta).

Propagator corrections dominate the electroweak observable contributions.

Abstract

We place constraints on the parameter space of the minimal supergravity (SUGRA) inspired supersymmetric (SUSY) extension of the standard model (SM), i.e. the mSUGRA model, by studying the loop-level contributions of supersymmetric particles to electroweak precision observables. In general the Higgs and superpartner particles of SUSY models contribute to electroweak observables through universal propagator corrections as well as process-specific vertex and box diagrams. However, because the mass of the lightest chargino is contrained to be greater than 91 GeV, we find that the process-dependent contributions to four-fermion amplitudes are negligibly small. Hence, the full analysis may be reduced to an analysis of the propagator corrections, and in some regions of parameter space the constraints from the (b ---> s gamma) process are quite important. The propagator corrections are dominated by the contributions of the scalar fermions, and we summarize the results in the Peskin-Takeuchi S-T plane and the contributions to the W-boson mass. We then present the results in the mSUGRA m_0 -- m_{1/2} plane and find that our analysis of the propagator corrections provides constraints in the small-m_0 -- small-m_{1/2} region, precisely the region of interest for collider phenomenology. In some regions of parameter space, especially for mu < 0 and large tan(beta), the constrained region is enlarged considerably by including the process (b ---> s gamma).