String GUTs

TL;DR

This paper explores how string theory can realize SUSY-GUT models like SU(5) and SO(10), analyzing their construction, features, and differences from traditional models, including the behavior of chiral fields and Higgs splitting.

Contribution

It demonstrates methods to build level 2 orbifold string models with GUT gauge groups and examines their generic features and phenomenological implications.

Findings

Constructed explicit level 2 orbifold models with SU(5) and SO(10) gauge groups.

Identified that chiral fields often act as string moduli without self-couplings.

Discussed mechanisms for doublet-triplet Higgs splitting in string-derived models.

Abstract

Standard SUSY-GUTs such as those based on $SU(5)$ or $SO(10)$ lead to predictions for the values of $\alpha _s$ and $sin^2\theta _W$ in amazing agreement with experiment. In this article we investigate how these models may be obtained from string theory, thus bringing them into the only known consistent framework for quantum gravity. String models with matter in standard GUT representations require the realization of affine Lie algebras at higher levels. We start by describing some methods to build level $k=2$ orbifold string models with gauge groups $SU(5)$ or $SO(10)$. We present several examples and identify generic features of the type of models constructed. Chiral fields appropriate to break the symmetry down to the standard model generically appear in the massless spectrum. However, unlike in standard SUSY-GUTs, they often behave as string moduli, i.e., they do not have self-couplings. We also discuss briefly the doublet-triplet Higgs splitting. We find that, in some models, built-in sliding-singlet type of couplings exist.