SU(5) D-brane realizations, Yukawa couplings and proton stability

TL;DR

This paper explores SU(5) GUT models within orientifold compactifications, addressing proton decay issues and Yukawa couplings, and proposes solutions involving additional D-brane stacks, with implications for model viability.

Contribution

It demonstrates that adding a U(1) D-brane stack can resolve proton decay and other problems in SU(5) D-brane models, and provides globally consistent constructions with instanton effects.

Findings

Two-stack Georgi-Glashow models face large proton decay rates.

Adding a U(1) D-brane stack mitigates phenomenological issues.

Flipped SU(5) models encounter severe drawbacks that are hard to overcome.

Abstract

We discuss SU(5) Grand Unified Theories in the context of orientifold compactifications. Specifically, we investigate two and three D-brane stack realizations of the Georgi-Glashow and the flipped SU(5) model and analyze them with respect to their Yukawa couplings. As pointed out in arXiv:0909.0271 the most economical Georgi-Glashow realization based on two stacks generically suffers from a disastrous large proton decay rate. We show that allowing for an additional U(1) D-brane stack this as well as other phenomenological problems can be resolved. We exemplify with globally consistent Georgi-Glashow models based on RCFT that these D-brane quivers can be indeed embedded in a global setting. These globally consistent realizations admit rigid O(1) instantons inducing the perturbatively missing coupling 10105^H. Finally we show that flipped SU(5) D-brane realizations even with multiple U(1) D-brane stacks are plagued by severe phenomenological drawbacks which generically cannot be overcome.