Scales of String Theory

TL;DR

This paper reviews the relationship between fundamental scales in string theory, discusses the brane-world scenario with large extra dimensions, and examines implications for gauge coupling unification.

Contribution

It introduces the extreme brane-world scenario with TeV scale and large extra dimensions, highlighting its naturalness and implications for unification puzzles.

Findings

Brane-world scenario with TeV scale and large transverse dimensions is plausible.

The scenario creates conditions similar to the energy desert.

Implications for gauge coupling unification are discussed.

Abstract

I review the arguments in favor of/against the traditional hypothesis that the Planck, string and compactification scales are all within a couple of orders of magnitude from each other. I explain how the extreme brane-world scenario, with TeV type I scale and two large (near millimetric) transverse dimensions, creates conditions analogous to those of the energy desert and is thus naturally singled out. I comment on the puzzle of gauge coupling unification in this context.