TASI 2004 Lectures: To the Fifth Dimension and Back
Raman Sundrum
TL;DR
The lectures present a mechanism-centered tour of extra dimensions, showing how 5D theories compactified on circles or intervals yield 4D gauge fields, scalars, fermions, and gravity through KK decomposition, with masses m_n = n/R and a radion modulus. They explore the Hosotani mechanism for gauge-symmetry breaking, chirality realization via orbifolds and brane-localized matter, and the matching of 5D to 4D couplings, all within the framework of non-renormalizable EFTs. A key thread is the emergence of Higgs-like scalars as extra-dimensional components of gauge fields, protected by higher-dimensional gauge symmetry, and the stabilization of moduli through quantum and classical (Goldberger-Wise) effects. The discussion culminates in warped extra dimensions (RS1/RS2) where the warp factor generates large hierarchies, localizes gravity, and yields TeV-scale KK gravitons and naturally hierarchical fermion couplings, offering tangible collider phenomenology and a tractable EFT regime guided by AdS/CFT intuition.
Abstract
Introductory lectures on Extra Dimensions delivered at TASI 2004. The emphasis is on basic mechanisms rather than specific models.