Time scales for nonlinear processes in preheating after multifield inflation with nonminimal couplings

Abstract

We have conducted extensive lattice simulations to study the post-inflation dynamics of multifield models involving nonminimal couplings. We explore the parameter dependence of preheating in these models and describe the various timescales that control such nonlinear processes as energy transfer, re-scattering, and the approach to radiation-domination and thermalization. In the limit of large nonminimal couplings (ξ I ∼ 100), we find that efficient transfer of energy from the inflaton condensate to radiative degrees of freedom, emergence of a radiation-dominated equation of state, and the onset of thermalization each consistently occur within N reh 3 e-folds after the end of inflation, largely independent of the values of the other couplings in the models. The exception is the case of negative ellipticity, in which there is a misalignment between the dominant direction in field-space along which the system evolves and the larger of the nonminimal couplings ξ I. In those cases, the field-space-driven parametric resonance is effectively shut off. More generally, the competition between the scalar fields' potential and the field-space manifold structure can yield interesting phenomena such as two-stage resonances. Across many regions of parameter space, we find efficient rescattering between the distinct fields, leading to a partial memory loss of the shape of the initial fluctuation spectrum. Despite the explosive particle production, which can lead to a quick depletion of the background energy density, the nonlinear processes do not induce any super-horizon correlations after the end of inflation in these models, which keeps predictions for CMB observables unaffected by the late-time amplification of isocurvature fluctuations. Hence the excellent agreement between primordial observables and recent observations is preserved for this class of models, even when we consider post-inflation dynamics.

The First Three Seconds: a Review of Possible Expansion Histories of the Early Universe

“…For large dimensionless nonminimal couplings ξ I ≥ O(10 2 ), as one finds in popular models like Higgs inflation [142], these couplings can yield especially efficient resonances at the end of inflation [143,144,145,146,147,148,149,150,151,152,153,154]. The rapid production of particles with wavenumber k ≥ H can drive w → 1/3 within ∆N rad ∼ O(1) after the end of inflation [155,156].…”

Primordial dark matter from curvature induced symmetry breaking

“…For quantum fields in curved spaces a non-minimal coupling to curvature generically emerges [20][21][22]. Such couplings have non-trivial implications for inflation [23][24][25][26] and importantly, as was shown in Refs. [27][28][29][30][31][32][33], non-minimal curvature terms can source matter generation.…”

Characterizing the post-inflationary reheating history, Part I: single daughter field with quadratic-quadratic interaction

“…in [44][45][46][47][48][49]. Twofield models with non-minimal gravitation couplings have been studied in detail with lattice simulations in [42,43], showing that for quartic potentials and quadratic-quadratic interactions RD can be achieved in 3 e-folds after inflation for generic coupling choices. Scenarios of geometric preheating where spectator fields are non-minimally coupled to gravity represent also interesting cases to be considered [69][70][71][72].…”

“…A fitting study for quadratic and quartic potentials was also carried out in [41], where the dynamics was characterized as a function of the coupling strength. Furthermore, lattice studies of multifield models with non minimal couplings to gravity, transformed into non-minimal kinetic terms in the Einstein frame, have been carried out in [42,43], see also [44][45][46] for semi-analytical studies. Other works on preheating with non-minimal kinetic terms include [47] in the context of DBI inflation and based on lattice simulations, and [48] and [49] in the context of α-attractor scenarios, based on lattice simulations and in semi-analytical computations, respectively.…”