SU(5) Grand Unification in Extra Dimensions and Proton Decay

TL;DR

This paper investigates proton decay within a 5D SUSY SU(5) GUT realized on the orbifold $S^1/(Z_2\times Z_2')$, with gauge/Higgs fields in the bulk and matter fields confined to fixed-brane loci. The authors show that appropriate brane parity assignments naturally suppress or forbid proton decay while preserving SU(5)-related fermion mass structures and allowing Majorana masses for neutrinos, maintaining a viable see-saw mechanism. The model solves the doublet-triplet splitting problem via boundary conditions and retains key predictions like gauge coupling unification and $m_b=m_\tau$ at the GUT scale, with neutrino masses and mixing compatible with the SU(5) framework. While promising, the authors acknowledge open issues such as SUSY breaking, detailed fermion mass fitting, and threshold corrections, outlining a straightforward path toward a realistic higher-dimensional GUT.

Abstract

We analyse proton decay in the context of simple supersymmetric SU(5) grand unified models with an extra compact spatial dimension described by the orbifold S^1/(Z_2 x Z_2'). Gauge and Higgs degrees of freedom live in the bulk, while matter fields can only live at the fixed point branes. We present an extended discussion of matter interactions on the brane. We show that proton decay is naturally suppressed or even forbidden by suitable implementations of the parity symmetries on the brane. The corresponding mechanism does not affect the SU(5) description of fermion masses also including the neutrino sector, where Majorana mass terms remain allowed.