Gravitational reheating in quintessential inflation

Abstract

We provide a detailed study of gravitational reheating in quintessential inflation generalizing previous analyses only available for the standard case when inflation is followed by an era dominated by the energy density of radiation. 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 calculate numerically the amount of the radiation energy density, and determine the temperature T * at which radiation starts dominating over kination. The value of T * is controlled by the Hubble parameter H0 during inflation and the transition time ∆t, scaling as H 2 0 [ln(1/H0∆t)] 3/4 for H0∆t ≪ 1 and H 2 0 (H0∆t) −c for H0∆t ≫ 1. The model-dependent parameter c is found to be around 0.5 in two different parametrizations for the transition between inflation and kination.

Reheating via gravitational particle production in the kination epoch

“…In our approach, we used particle creation during the stiff matter dominated era in contrast to previous studies where the particle creation has been obtained by a change of metric. This difference in the models does not therefore allow a direct comparison of results, because in the previous studies the reheating temperature usually depends on the inflation scale and the transition time from inflation to kination [12]. Our model is independent of such parameters and offers a numerical value to the reheating temperature.…”

“…An early stiff matter era was presumably first considered by Zel'dovich [8] and indeed, the stiff equation of state in of itself exhibits several interesting cosmological properties worth of further investigation [9,10]. Reheating in a kination epoch has received quite a bit of interest lately and numerous new studies have been done [11][12][13][14][15][16]. Most of these studies are concerned with quintessence models incorporating a period of kination and the particle production is obtained through a change of metric from de Sitter to post-inflationary metric.…”

Gravitational reheating in quintessential inflation

“…In the above expression m P is the Plank mass, g I, * are the numbers of relativistic degrees of freedom at T I, * while the combination I expression can be found in [1], is plotted in Fig. 1 in terms of the transition time H 0 ∆t for the two cases when the transition is modeled according to Eqs.…”

“…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.…”