New Dimensions at a Millimeter to a Fermi and Superstrings at a TeV

TL;DR

Antoniadis, Arkani-Hamed, Dimopoulos, and Dvali embed the ADD large extra dimensions proposal into perturbative Type I string theory with SM on D3-branes and gravity in the bulk at a TeV scale. They show that a large internal volume and T-duality can reproduce the observed Planck and gauge couplings within a calculable framework, yielding testable collider and gravity signatures. The work identifies two main phenomenological signals—Regge excitations of SM states and emission of higher-dimensional gravitons—while addressing model-building issues such as proton stability, gauge coupling unification, and SUSY breaking. Overall, the paper provides a concrete string-theoretic realization of TeV-scale quantum gravity and outlines its experimental implications for the LHC, NLC, and precision gravity tests.

Abstract

Recently, a new framework for solving the hierarchy problem has been proposed which does not rely on low energy supersymmetry or technicolor. The gravitational and gauge interactions unite at the electroweak scale, and the observed weakness of gravity at long distances is due the existence of large new spatial dimensions. In this letter, we show that this framework can be embedded in string theory. These models have a perturbative description in the context of type I string theory. The gravitational sector consists of closed strings propagating in the higher-dimensional bulk, while ordinary matter consists of open strings living on D3-branes. This scenario raises the exciting possibility that the LHC and NLC will experimentally study both ordinary aspects of string physics such as the production of narrow Regge-excitations of all standard model particles, as well more exotic phenomena involving strong gravity such as the production of black holes. The new dimensions can be probed by events with large missing energy carried off by gravitons escaping into the bulk. We finally discuss some important issues of model building, such as proton stability, gauge coupling unification and supersymmetry breaking.