Grand Unification in RS1
Kaustubh Agashe, Antonio Delgado, Raman Sundrum
TL;DR
This work investigates gauge coupling unification in a non-supersymmetric RS1 setup with gauge fields and fermions in the bulk. It shows that one-loop, warping-aware running yields a robust logarithmic dependence on the unification scale $M_{GUT}$ with small, volume-enhanced bulk threshold corrections, making high-scale unification feasible. A mechanism based on an extra bulk $\mathrm{U}(1)$ symmetry suppresses proton decay via boundary-condition breaking of the unified group, and the authors discuss a 4D AdS/CFT dual interpretation of the results. The study argues that RS1 unification can operate alongside a non-supersymmetric solution to the hierarchy problem, offering a calculable alternative to SUSY-based unification with a comparable qualitative fit to observed couplings.
Abstract
We study unification in the Randall-Sundrum scenario for solving the hierarchy problem, with gauge fields and fermions in the bulk. We calculate the one-loop corrected low-energy effective gauge couplings in a unified theory, broken at the scale M_GUT in the bulk. We find that, although this scenario has an extra dimension, there is a robust (calculable in the effective field theory) logarithmic dependence on M_GUT, strongly suggestive of high-scale unification, very much as in the (4D) Standard Model. Moreover, bulk threshold effects are naturally small, but volume-enhanced, so that we can accommodate the measured gauge couplings. We show in detail how excessive proton decay is forbidden by an extra U(1) bulk gauge symmetry. This mechanism requires us to further break the unified group using boundary conditions. A 4D dual interpretation, in the sense of the AdS/CFT correspondence, is provided for all our results. Our results show that an attractive unification mechanism can combine with a non-supersymmetric solution to the hierarchy problem.