Doublet-Triplet Splitting in Fertile Left-Right Symmetric Heterotic String Vacua

TL;DR

This paper develops a new classification method for Left-Right Symmetric heterotic-string vacua, significantly increasing the efficiency of finding phenomenologically viable models and identifying a doublet-triplet splitting mechanism in string theory.

Contribution

It introduces a targeted classification approach based on fertile cores, boosting the probability of finding viable models by nine orders of magnitude and revealing a doublet-triplet splitting mechanism.

Findings

Increased model generation efficiency by nine orders of magnitude.

Identification of a doublet-triplet splitting mechanism in twisted sectors.

Generated approximately 140,000 viable models.

Abstract

Classification of Left-Right Symmetric (LRS) heterotic-string vacua in the free fermionic formulation, using random generation of generalised GSO (GGSO) projection coefficients, produced phenomenologically viable models with probability $4\times 10^{-11}$. Extracting substantial number of phenomenologically viable models requires modification of the classification method. This is achieved by identifying phenomenologically amenable conditions on the Generalised GSO projection coefficients that are randomly generated at the $SO(10)$ level. Around each of these fertile cores we perform a complete LRS classification, generating viable models with probabilility $1.4\times 10^{-2}$, hence increasing the probability of generating phenomenologically viable models by nine orders of magnitude, and producing some $1.4\times 10^5$ such models. In the process we identify a doublet-triplet selection mechanism that operates in twisted sectors of the string models that break the $SO(10)$ symmetry to the Pati-Salam subgroup. This mechanism therefore operates as well in free fermionic models with Pati-Salam and Standard-like Model $SO(10)$ subgroups.