Intersecting Branes Flip SU(5)

TL;DR

The paper investigates flipped SU(5) × U(1)_X GUT realizations from intersecting D6-branes on toroidal orientifolds and orbifolds. While orientifolds with integer windings tend to yield many generations and fail to produce the flipped structure cleanly, toroidal orbifolds with fractional windings naturally accommodate three generations and flipped U(1)_X in several three-stack configurations. A key finding is that three-stack orbifold models can provide a three-generation fermion content with correct U(1)_X charges and either a complete electroweak Higgs sector or a GUT-breaking sector, but achieving both simultaneously without introducing extra chiral matter remains challenging. The authors suggest that breaking the GUT symmetry via higher-dimensional mechanisms, rather than embedding GUT Higgs multiplets in the chiral spectrum, may be the more viable path within these brane constructions. Overall, the work delineates the landscape of flipped SU(5) embeddings in intersecting-brane setups and highlights the balance between generation count, Higgs spectrum, and extra matter.

Abstract

Within a toroidal orbifold framework, we exhibit intersecting brane-world constructions of flipped SU(5) \times U(1) GUT models with various numbers of generations, other chiral matter representations and Higgs representations. We exhibit orientifold constructions with integer winding numbers that yield 8 or more conventional SU(5) generations, and orbifold constructions with fractional winding numbers that yield flipped SU(5) \times U(1) models with just 3 conventional generations. Some of these models have candidates for the 5 and {\bar 5} Higgs representations needed for electroweak symmetry breaking, but not for the 10 and {\bar 10} representations needed for GUT symmetry breaking. We have also derived models with complete GUT and electroweak Higgs sectors, but these have undesirable extra chiral matter.