Bouncing Galileon cosmologies

Abstract

We present nonsingular, homogeneous and isotropic bouncingsolutions of the conformal Galileon model. We show that suchsolutions necessarily begin with a radiation-dominated contractingphase. This is followed by a quintom scenario in which thebackground equation of state crosses the cosmological constantboundary allowing for a nonsingular bounce which in turn is followedby Galilean Genesis. We analyze the spectrum of cosmologicalperturbations in this background. Our results show that thefluctuations evolve smoothly and without any pathology, but theadiabatic modes form a blue tilted spectrum. In order to achieve ascale-invariant primordial power spectrum as required by currentobservations, we introduce a light scalar field coupling to theGalileon kinetically. We find two couplings which yield ascale-invariant spectrum, one of which requires a fine tuning of theinitial conditions. This model also predicts a blue tilted spectrumof gravitational waves stemming from quantum vacuum fluctuations inthe contracting phase.