LHC, SSC and the universe

Abstract

The geometric mean of the Planck mass and the 2.7 K background temperature — numerically equal to about a TeV — is the maximum mass that any cosmologically stable perturbatively coupled elementary particle can have or else the density of the universe exceeds its critical value. Thus, the TeV scale is cosmologically significant for reasons unrelated to the scale of electroweak symmetry breaking; it would persist even if the masses of the W and Z vanished. This implies that the TeV scale emerges cosmologically in many extensions of the standard model involving new particles and forces. We derive, for example, upper limits of order of a few TeV to the mass of the lightest supersymmetric particle LSP as well as to the masses of new U′(1) gauge bosons and their associated stable electroweak singlets that can occur in superstring theories. Any dark matter candidate that is perturbatively coupled must also weigh less than a few TeV. Thus, cosmology implies that all these particles should be accessible to multi-TeV colliders. In particular, the dominant dark component of the universe and its charged electroweak partners could be discovered in such machines. These ideas suggest a cosmological argument for a desert commencing near a TeV. They have implications for unified and superstring models. For example, new U′(1)'s accompanied by stable electroweak singlets have to be lighter than a few TeV; they therefore must commute with family rotations or else be in conflict with the K LK S mass difference.