Anomaly-induced gauge unification and brane/bulk couplings in gravity-localized theories

It has recently been proposed that gravity-localized compactifications can generate the required gauge hierarchy without the need for hierarchically l arge extra space-time dimensions. In this paper, we show that gauge couplin g 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 com pactifications, including an inability to accommodate the GUT scale and the electroweak scale simultaneously. We also show that brane/bulk couplings i n this scenario are generically too small to be phenomenologically relevant . Finally, we speculate on possible resolutions to these puzzles. (C) 2000 Elsevier Science B.V. All rights reserved.