Neutralino relic density in a universe with a nonvanishing cosmological constant

Abstract

We discuss the relic density of the lightest of the supersymmetric particles in view of new cosmological data, which favor the concept of an accelerating universe with a nonvanishing cosmological constant. Recent astrophysical observations provide us with very precise values of the relevant cosmological parameters. Certain of these parameters have direct implications on particle physics, e.g., the value of matter density, which in conjunction with electroweak precision data put severe constraints on the supersymmetry breaking scale. In the context of the constrained minimal supersymmetric standard model (CMSSM) such limits read as ${M}_{1/2}\ensuremath{\simeq}300\mathrm{GeV}--340\mathrm{}\mathrm{GeV},$ ${m}_{0}\ensuremath{\simeq}80\mathrm{GeV}--130\mathrm{}\mathrm{GeV}.$ Within the context of the CMSSM a way to avoid these constraints is either to go to the large $\mathrm{tan}\ensuremath{\beta}$ and $\ensuremath{\mu}>0$ region, or make ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{R},$ the next to lightest supersymmetric particle (LSP), be almost degenerate in mass with the LSP.