Enlarging mSUGRA parameter space by decreasing pre-BBN Hubble rate in Scalar-Tensor Cosmologies

TL;DR

This paper explores how scalar-tensor cosmologies with multiple matter sectors can significantly reduce the pre-BBN Hubble rate, enlarging dark matter relic abundance predictions and impacting collider phenomenology.

Contribution

It demonstrates conditions under which scalar-tensor theories can lower the early universe expansion rate, expanding the parameter space for dark matter models.

Findings

Reduced Hubble rate up to two orders of magnitude before BBN.

Enlarged cosmologically allowed regions in supergravity models.

Implications for LHC neutralino searches.

Abstract

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 fixed point towards General Relativity at late times. Instead, when additional matter sectors with different 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 field evolution, a sizeable reduction (up to about 2 orders of magnitude) of the Hubble rate prior to Big Bang 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 significantly enlarged, implying a change in the potential reach of LHC on the neutralino phenomenology.