Is SUSY Natural?

Abstract

Spacetime supersymmetry is widely believed to play an important role in most fundamental theories of physics, and is usually invoked in order to address problems of naturalness. In this paper, we examine the question of whether supersymmetry itself is ``natural'' (i.e., likely to exist as a fundamental component of nature at high energy scales). Our approach to answering this question is based on a statistical examination of the heterotic string landscape, and our conclusion is that supersymmetry is an exceedingly rare phenomenon. We also find that the likelihood of supersymmetry appearing at the string scale is dependent on the gauge symmetries present at the string scale, with certain gauge groups strongly favoring the appearance of N=1 supersymmetry and others not. This article summarizes several recent papers, yet also contains some new results. In particular, one new result is that the heterotic landscape appears to favor either the non-supersymmetric Standard Model or an N=1 SUSY GUT gauge group at the string scale; by contrast, the opposite outcomes (namely the MSSM or a non-supersymmetric GUT) are significantly disfavored.

9 pages, LaTeX, 3 tables. Invited article to appear in the New Journal of Physics, Special Focus Issue "Particle Physics at the TeV Scale"

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• de Sitter Vacua in String Theory
• The statistics of string/M theory vacua
• Is There A String Theory Landscape
• Statistics on the Heterotic Landscape: Gauge Groups and Cosmological Constants of Four-Dimensional Heterotic Strings
• A New Handle on de Sitter Compactifications
• Supersymmetry versus Gauge Symmetry on the Heterotic Landscape
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• Genetic Algorithms and the Search for Viable String Vacua
• Stability, enhanced gauge symmetry and suppressed cosmological constant in 9D heterotic interpolating models
• Naturalness versus stringy naturalness (with implications for collider and dark matter searches)
• Building a Nest at Tree Level: Classical Metastability and Non-Trivial Vacuum Structure in Supersymmetric Field Theories
• Correlation Classes on the Landscape: To What Extent is String Theory Predictive?
• Free Fermionic Heterotic Model Building and Root Systems
• Note on a NAHE Variation
• A Non-Standard String Embedding of E8