Enlarging minimal-Supergravity parameter space by decreasing pre-Nucleosynthesis Hubble rate in Scalar-Tensor Cosmologies

We determine under what conditions Scalar Tensor cosmologies predict an expansion rate which is reduced as compared to the standard General Relativity case. We show that ST theories with a single matter sector typically predict an enchanced Hubble rate in the past, as a consequence of the requirement of an attractive xed point towards General Relativity at late times. Instead, when additional matter sectors with dieren t conformal factors are added, the late time convergence to General Relativity is mantained and at the same time a reduced expansion rate in the past can be driven. For suitable choices of the parameters which govern the scalar eld evolution, a sizeable reduction (up to about 2 orders of magnitude) of the Hubble rate prior to Big Bag Nucleosynthesis can be obtained. We then discuss the impact of these cosmological models on the relic abundance of dark matter is minimal Supergravity models: we show that the cosmologically allowed regions in parameter space are signican tly enlarged, implying a change in the potential reach of LHC on the neutralino phenomenology.