Defrosting in an emergent Galileon cosmology

We study the transition from an emergent Galileon condensate phase of the early universe to a later expanding radiation phase. This defrosting or preheating transition is a consequence of the excitation of matter fluctuations by the coherent Galileon condensate, in analogy to how preheating in inflationary cosmology occurs via the excitation of matter fluctuations through coupling of matter with the coherent inflaton condensate. We show that the minimal coupling of matter (modeled as a massless scalar field) to the Galileon field introduced by Creminelli, Nicolis, and Trincherini in order to generate a scale-invariant spectrum of matter fluctuations is sufficient to lead to efficient defrosting, provided that the effects of the nonvanishing expansion rate of the universe are taken into account. If we neglect the effects of expansion, an additional coupling of matter to the Galileon condensate is required. We study the efficiency of the defrosting mechanism in both cases.