Anomaly-Induced Gauge Unification and Brane/Bulk Couplings in Gravity-Localized Theories

TL;DR

This work shows that gravity-localized compactifications with a warp factor can naturally yield gauge coupling unification via a warp-induced rescaling anomaly on the Standard-Model brane, effectively mimicking traditional high-scale unification without a hidden running sector. It analyzes two warp-sign scenarios, finding that a negative-$k$ (blue-shifted) setup can accommodate GUT-scale physics and potentially realistic neutrino masses, yet both signs face difficulties reconciling the electroweak scale with unification on a single brane. The authors discuss the limitations of brane/bulk couplings in these models and propose avenues (e.g., modified warp profiles, low-scale seesaw) to resolve tensions, highlighting the intriguing but incomplete viability of gravity-localized unification. Overall, the paper uncovers a novel anomaly-based mechanism for unification tied to extra-dimensional geometry, while revealing competing constraints that any fully realistic model must address.

Abstract

It has recently been proposed that gravity-localized compactifications can generate the required gauge hierarchy without the need for hierarchically large extra spacetime dimensions. In this paper, we show that gauge coupling unification arises naturally in such scenarios as a result of the anomaly induced by the rescaling of the wavefunctions of the brane fields. Thus, ``anomaly-induced'' gauge coupling unification can easily explain the apparent low-energy gauge couplings in gravity-localized compactifications. However, we also point out a number of phenomenological difficulties with such compactifications, including an inability to accommodate the GUT scale and the electroweak scale simultaneously. We also show that brane/bulk couplings in this scenario are generically too small to be phenomenologically relevant. Finally, we speculate on possible resolutions to these puzzles.