TeV Scale Superstring and Extra Dimensions

TL;DR

The paper argues that a TeV-scale string paradigm, realized in Type I string theory with brane-localized gauge fields and gravity propagating in extra bulk dimensions, can reconcile gauge and gravity couplings at low scales while satisfying proton-decay constraints. It formalizes the brane-world setup, derives relations among the string scale, compactification volumes, and Planck mass, and analyzes how large extra dimensions can coexist with perturbative gauge couplings. Through explicit 4D ${\cal N}=1$ Type I models with Pati-Salam-like gauge structures, it demonstrates multiple viable scenarios for embedding the Standard Model and explains how custodial U(1) symmetries can suppress proton decay and protect baryon number. The results suggest distinctive experimental signatures of TeV-scale strings and large extra dimensions, offering a testable alternative to conventional GUT/Planck-scale unification.

Abstract

Utilizing the idea of extra large dimensions, it has been suggested that the gauge and gravity couplings unification can happen at a scale as low as 1 TeV. In this paper, we explore this phenomenological possibility within string theory. In particular, we discuss how the proton decay bound can be satisfied in Type I string theory. The string picture also suggests different scenarios of gauge and gravitational couplings unification. The various scenarios are explicitly illustrated with a specific 4-dimensional N=1 supersymmetric chiral Type I string model with Pati-Salam-like gauge symmetry. We point out certain features that should be generic in other Type I strings.