Violent preheating in inflation with nonminimal coupling

Abstract

We study particle production at the preheating era in inflation models with nonminimal coupling ξφ 2 R and quartic potential λφ 4 /4 for several cases: real scalar inflaton, complex scalar inflaton and Abelian Higgs inflaton. We point out that the preheating proceeds much more violently than previously thought. If the inflaton is a complex scalar, the phase degree of freedom is violently produced at the first stage of preheating. If the inflaton is a Higgs field, the longitudinal gauge boson production is similarly violent. This is caused by a spike-like feature in the time dependence of the inflaton field, which may be understood as a consequence of the short time scale during which the effective potential or kinetic term changes suddenly. The produced particles typically have very high momenta k √ λM P . The production might be so strong that almost all the energy of the inflaton is carried away within one oscillation for ξ 2 λ O(100). This may partly change the conventional understandings of the (p)reheating after inflation with the nonminimal coupling to gravity such as Higgs inflation. We also discuss the possibility of unitarity violation at the preheating stage.

Dynamical emergence of scalaron in Higgs inflation

“…It still seems to require that the Higgs inflation should be UV completed below the Planck scale. More interestingly, the unitarity could be violated during preheating [15][16][17], resulting in the necessity of UV completion to describe the reheating dynamics. These are the (very) rough sketch of the unitarity issue on the Higgs inflation in literature so far.…”

“…For instance, we can easily see in the Einstein frame (before the field redefinition) that the following one-loop diagram vanishes: where we have used the similarity since the right hand side includes the contributions from the spin-2 part of the graviton as well. 15 It is thus clear that the one-loop diagram (5.6) in the Einstein frame corresponds to many diagrams including the vacuum polarization, the vertex correction and the box diagrams in the Jordan frame. It means that the ξ-dependence cancels out among these diagrams in the Jordan frame.…”

Some like it hot: R2 heals Higgs inflation, but does not cool it

“…The crucial ingredient -the evolution of longitudinal components of the weak gauge bosonswas missed there. The dependence of this component on the external Higgs field (inflaton) turns out to be spiky [24][25][26], leading to violent production of longitudinal modes of the weak gauge bosons and very rapid reheating of the Universe. This finding is dangerous due to the strong coupling problem, since the reheating dynamics happen right inside the strong coupling domain, making any analysis unreliable.…”

Nonlinear Dynamics of Preheating after Multifield Inflation with Nonminimal Couplings

“…For ξ φ = 1, 10 parametric resonance due to the contribution from the potential to m 2 eff,χ leads to a slow growth of δχ fluctuations; these eventually rescatter, leading to the growth of δφ fluctuations and lowering the χ rms /φ rms ratio. For ξ φ ≥ 40 the "Ricci spike" [17,36] leads to a fast growth of δχ fluctuations. This is seen in Fig.…”