Gravitational reheating in quintessential inflation

Abstract

Abstract. Quintessential inflation assumes a common origin for inflation and the dark energy of the Universe. In this scenario reheating can occur through gravitational particle production during the inflation-kination transition. We provide a detailed study of gravitational reheating in quintessential inflation and determine the temperature T * at which radiation starts dominating over kination, generalizing previous analyses only available for the standard case when inflation is followed by an era dominated by the energy density of radiation, The value of T * is controlled by the Hubble parameter H0 during inflation and the transition time ∆t, scaling as H IntroductionIt is somehow intriguing that both periods of accelerated expansion of the Universe we are aware of, i.e. inflation and Dark Energy, can be explained by some scalar field, the inflaton and quintessence respectively, whose potential energy dominates the energy density at some time of its evolution, so it is natural to imagine to unify the two scenarios, identifying the inflaton and quintessence with the same field φ. As a consequence of this, various models of quintessential inflation have been discussed in the literature (see references in [1]). In the quintessential inflation scenario two main qualitative properties emerge: i) The potential V (φ) needs to account for the large mismatch between the inflationary plateau V 0 at the beginning of the φ field evolution and the tiny scale V f of the quintessential tail eventually accounting for the cosmological constant today, so that at the end of its slow-roll phase the field φ experiences a strong acceleration as it "deep-dives" from V 0 toward V F . Thus the Universe undergoes a period of "kination" expansion when its energy density is dominated by the kinetic energy of φ. ii) In this scenario the standard reheating mechanism which is usually assumed to create the initial plasma by the decay of φ is not at work, but the mechanism of gravitational particle production is able to reheat the Universe. In this talk I will summarize the results of [1], where a quantitative analysis for the amount of particle production through gravitational reheating is provided, generalizing the analysis of Ref. [2], where the same discussion was restricted to the case of the inflation-radiation transition. The actual value of T * has important phenomenological consequences. For instance it may change the predictions for the relic density of a thermal cold dark matter candidate or the thermal leptogenesis induced by the CP-violating decay of a right-handed neutrino.