Is SUSY Natural?

TL;DR

This paper investigates the naturalness of supersymmetry by statistically analyzing the heterotic string landscape, finding that supersymmetry is rare and its likelihood depends on specific gauge symmetries, with certain models being favored.

Contribution

It provides a statistical assessment of supersymmetry's naturalness in string theory, revealing its rarity and dependence on gauge groups, and introduces new insights into the favored string landscape configurations.

Findings

Supersymmetry is an exceedingly rare phenomenon in the heterotic string landscape.

Likelihood of supersymmetry depends on gauge symmetries at the string scale.

The landscape favors non-supersymmetric Standard Model or N=1 SUSY GUT at the string scale.

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.