SU(5) Unified Theories from Intersecting Branes

TL;DR

This paper presents the first string theory models of three-generation non-supersymmetric SU(5) and flipped SU(5) GUTs derived from intersecting D-branes, which break to the Standard Model without extra matter or gauge groups.

Contribution

It constructs explicit intersecting brane models realizing realistic GUTs with features like neutrino see-saw, proton decay suppression, and natural doublet-triplet splitting.

Findings

Realization of three-generation non-supersymmetric SU(5) GUTs from string theory.

Implementation of neutrino see-saw mechanism within these models.

Proton decay can be suppressed by high GUT scale and scalar mass stability.

Abstract

We discuss the first string theory examples of three generation non-supersymmetric SU(5) and {\em flipped} SU(5) GUTS, which break to the Standard model at low energy, without extra matter and/or gauge group factors. Our GUT examples are based on IIA $Z_3$ orientifolds with D6-branes intersecting at non-trivial angles. These theories necessarily satisfy RR tadpoles and are free of NSNS tadpoles as the complex structure moduli are frozen (even though a dilaton tadpole remains) to discrete values. We identify appropriately the bifundamental Higgses responsible for electroweak symmetry breaking. In this way, the neutrino see-saw mechanism get nicely realized in these constructions. Moreover, as baryon number is not a gauged symmetry gauge mediated dimension six operators do contribute to proton decay; however proton lifetime may be safely enhanced by appropriately choosing a high GUT scale. An accompanying natural doublet-triplet splitting guarantees the suppression of scalar mediated proton decay modes and the stability of triplet scalar masses against higher dimensional non-renormalizable operators.