How could (should) we make contact between string/M-theory and our four-dimensional world, and associated LHC predictions?

Abstract

String/M-theory is an exciting framework within which we try to understand our universe and its properties. Compactified string/M-theories address and offer solutions to almost every important question and issue in particle physics and particle cosmology. But earlier goals of finding a top–down “vacuum selection” principle and deriving the 4D theory have not yet been realized. Does that mean we should stop trying, as nearly all string theorists have? Or can we proceed in the historical way to make a few generic, robust assumptions not closely related to observables, and follow where they lead to testable predictions and explanations? Making only very generic assumptions is a significant issue. I discuss how to try to proceed with this approach, particularly in M-theory compactified on a 7D manifold of G2 holonomy. One goal is to understand our universe as a string/M-theory vacuum for its own sake, in the long tradition of trying to understand our world, and what that implies. In addition, understanding our vacuum may be a prelude to understanding its connection to the multiverse.