Quasi-Supersymmetric $G^3$ Unification from Intersecting D6-Branes on Type IIA Orientifolds

TL;DR

This work constructs three quasi-supersymmetric $G^3$ grand unified models from intersecting D6-branes on Type IIA orientifolds with an $S_3$ symmetry, embedding the Standard Model fermions and Higgs into bifundamentals while preserving RR tadpole cancellation via an auxiliary D6-brane. The observable sector remains $N=1$ SUSY, but SUSY is broken by the auxiliary brane, allowing gauge coupling unification to be achieved through equal complex structure moduli and light open-string states that break $G^3$ to the SM. For Model I with $U(4)^3$ and $oldsymbol extchi=1$, the string scale is around $M_s oughly 5.6 imes 10^{11}$ GeV and the unified coupling is small ($ obreak obreak obreak $ obreak $), indicating a need to address RG-running tuning and potential NSNS tadpole issues; nonetheless, the framework offers a concrete path to GUTs with realistic chiral spectra and a mechanism for symmetry breaking via light string states. The results highlight a viable but delicate interplay between geometry, SUSY breaking, and gauge unification in brane-world constructions, motivating further exploration of the phenomenological viability and higher-scale consistency of such models.

Abstract

We construct three quasi-supersymmetric $G^3$ GUT models with $S_3$ symmetry and gauge coupling unification from intersecting D6-branes on Type IIA orientifolds. The Standard Model fermions and Higgs doublets can be embedded into the bifundamental representations in these models, and there is no any other unnecessary massless representation. Especially in Model I with gauge group $U(4)^3$, we just have three-family SM fermions and three pairs of Higgs particles. The $G^3$ gauge symmetry in these models can be broken down to the Standard Model gauge symmetry by introducing light open string states. And 1 TeV scale supersymmetry breaking soft masses imply the reasonable intermediate string scale.