Constraining the early Hubble rate using Cosmic Antiprotons

Many interesting cosmological models predict an enhancement of the Hubble expansion rate in the early Universe. Among these are some braneworld models, models with a kination phase and scalar-tensor models. In this paper we show that the pre–Big–Bang–Nucleosynthesis (pre-BBN) enhancement can be strongly constrained by the combined use of the bounds on the Dark Matter relic density and antiproton production. For a Dark Matter particle of 100 GeV the maximal enhancement of the Hubble rate ranges from a few up to a factor of 30.