Neutralino Relic Density with a Cosmological Constant confronts Electroweak Precision Measurements

We discuss the relic density of the lightest of the supersymmetric particles (LSP) in view of new cosmological data, which favour the concept of an accelerating Universe with a non-vanishing cosmological constant. The new bound on the Cold Dark Matter density, ΩCDMh 2 0 . 0.22, puts stringent constraints on supersymmetry preferring low supersymmetry breaking scales, in sharp contrast to electroweak precision measurements favouring large supersymmetry breaking scales. Supersymmetric predictions are in agreement with cosmological data and electroweak precision data in the window of the parameter space: m0 < 200 GeV, 300 GeV < M1/2 < 400 GeV, putting bounds on sparticle masses, which may be evaded if m LSP < mτ̃R . 1.2 mLSP. Recent observations of type Ia supernovae (SNIa) put new constraints on the cosmological parameters. The data favour an almost flat and accelerating Universe, where the acceleration mainly is driven by a non-vanishing cosmological constant. There is a growing consensus that the anisotropy of the Cosmic Background Radiation (CBR) offers the best way to determine the curvature of the Universe and hence the total matter-energy density Ω0 [1]. The data are consistent with a flat Universe, since Ω0 = 1.0±0.2 [1,2], and the radiation content of the matter-energy density, that is contribution coming from CBR and/or ultra relativistic neutrinos, is very small. Therefore the present matter-energy density can be decomposed basically into two components: the matter density ΩM and the vacuum energy ΩΛ: