Grand Unified Theories and Supersymmetry in Particle Physics and Cosmology

Abstract

A review is given on the consistency checks of GUT, which unify the electroweak and strong nuclear forces into a single theory. Such theories predict a new kind of force, which could provide answers to several open questions in cosmology. The possible role of such a ``primeval'' force will be discussed in the framework of the Big Bang Theory. Although such a force cannot be observed directly, there are several predictions of GUT's, which can be verified at low energies. The MSSM distinguishes itself from other GUT's by a successful prediction of many unrelated phenomena with a minimum number of parameters. Among them: a) Unification of the couplings constants; b) Unification of the masses; c) Existence of dark matter; d) Proton decay; e) electroweak symmetry breaking at a scale far below the unification scale. A combined fit shows that indeed the MSSM model can satisfy all these constraints simultaneously. The corresponding constraints on the as yet unknown top mass, the strong coupling constant, and all SUSY masses are given within the minimal model, taking into account the complete second order RGE's for the couplings and the one-loop corrected Higgs potential for the calculation of the Z and the Higgs masses.