Posted: May 16, 2017 4:35 pm
DavidMcC wrote:Randall and Sundrum's theory is the brane-world idea, that universes start in a manner akin to a bumper-to-bumper collision on a packed motorway (which is where they were when they came up with their model). It doesn't seem very natural to me! I much prefer the Lee Smolin idea that universes are black holes as seen from within their own space.
No. You need to (re-)read their paper, it's based on a model with 4 space + 1 time dimensions. (Whether the 4th space dimension is infinite in extent or bounded is part of the model's development in later work.)
We propose a new higher-dimensional mechanism for solving the Hierarchy Problem. The Weak scale is generated from a large scale of order the Planck scale through an exponential hierarchy. However, this exponential arises not from gauge interactions but from the background metric (which is a slice of AdS_5 spacetime). This mechanism relies on the existence of only a single additional dimension. We demonstrate a simple explicit example of this mechanism with two three-branes, one of which contains the Standard Model fields. The experimental consequences of this scenario are new and dramatic. There are fundamental spin-2 excitations with mass of weak scale order, which are coupled with weak scale as opposed to gravitational strength to the standard model particles. The phenomenology of these models is quite distinct from that of large extra dimension scenarios; none of the current constraints on theories with very large extra dimensions apply.
arxiv link