J un 2 00 9 SUSY Constraints , Relic Density , and Very Early Universe

The sensitivity of the lightest supersymmetric particle relic density calculation to different cosmological scenarios is discussed. In particular, we show that a modification of the expansion rate or of the entropy content of the Universe before Big-Bang nucleosynthesis can completely modify the relic density constraints on the SUSY parameter space, and we propose a general parametrization to study the effects of these modifications. We also show that using the relic density in the context of supersymmetric constraints is highly questionable since its calculation relies on model-dependent assumptions. On the other hand, we notice that combining the relic density calculation with the future discoveries of the LHC will hopefully give light on the Very Early Universe properties. Cosmological observations reveal that the massive content of the Universe is mostly composed of dark matter of unknown – but non-baryonic – nature. New physics models, such as supersymmetry (SUSY), provide stable particle candidates for dark matter, and one can compute their present energy density, generally referred as relic density [1, 2]. This relic density is often compared to the dark matter density deduced from cosmological observations in order to constrain new physics parameters [3,4]. The main assumption in doing that is that the Universe is ruled by the standard model of cosmology, which assumes that radiation energy and entropy Electronic address: [email protected] Electronic address: [email protected]