We review the construction and properties of four dimensional string models, using free fermions on the world-sheet. We prove that as opposed to gauge symmetries, broken space-time supersymmetry can only be restored continuously by decompactification.

The standard model of particle physics is analyzed for the case of a Higgs potential not favoring spontaneous electroweak symmetry breaking to gain insight into the physics of the standard model. Electroweak breaking still takes place, and quarks and leptons still acquire masses but through bosonic technicolor. This " other " phase of the standard model exhibits interesting phenomena.

We discuss the capabilities of future muon col-liders to resolve important particle physics questions. A collider with c.m. energy √ s = 100 to 500 GeV offers the unique opportunity to produce Higgs bosons in the s-channel and thereby measure the Higgs masses, total widths and several partial widths to high precision. At this same machine, tt and W + W − threshold studies would yield superior p...

The status of internal symmetry breaking at high temperature in supersymmetric models is reviewed. This phenomenon could solve some well known cosmological problems, such as the domain wall, monopole and false vacuum problems.

The μ parameter is calculated in supergravity models possessing the U(1)A× U(1)R symmetry. In one natural model without a free mass parameter below the Planck scale, the symmetry breaking scale is identified as the hidden sector squark condensation scale. [email protected] 1