Neutralino relic density in a universe with a nonvanishing cosmological constant - art. no. 023515

We discuss the relic density of the lightest of the supersymmetric particle s in view of new cosmological data, which favor the concept of an accelerat ing universe with a nonvanishing cosmological constant. Recent astrophysica l observations provide us with very precise values of the relevant cosmolog ical parameters. Certain of these parameters have direct implications on pa rticle physics, e.g., the value of matter density, which in conjunction wit h electroweak precision data put severe constraints on the supersymmetry br eaking scale. In the context of the constrained minimal supersymmetric stan dard model (CMSSM) such limits read as M-1/2 similar or equal to 300 GeV-34 0 GeV, m(0) similar or equal to 80 GeV-130 GeV. Within the context of the C MSSM a way to avoid these constraints is either to go to the large tan beta and mu > 0 region, or make (T) over tilde(R), the next to lightest supersy mmetric particle (LSP), be almost degenerate in mass with the LSP.