Preheating after Techni-inflation

Physical Review D, 1999

We investigate a resonant particle production of a scalar field χ coupled non-minimally to a spacetime curvature R (ξRχ 2 ) as well as to an inflaton field φ (g 2 φ 2 χ 2 ). In the case of g < ∼ 3 × 10 −4 , ξ effect assists g-resonance in certain parameter regimes. However, for g > ∼ 3 × 10 −4 , g-resonance is not enhanced by ξ effect because of ξ suppression effect as well as a back reaction effect. If ξ ≈ −4, the maximal fluctuation of produced χ-particle is χ 2 max ≈ 2 × 10 17 GeV for g < ∼ 1 × 10 −5 , which is larger than the minimally coupled case with g ≈ 1 × 10 −3 . 98.80.Cq, 05.70.Fh, 11.15.Kc * electronic address:[email protected] † electronic address:[email protected] ‡ electronic address:[email protected] ticles [ . This initial evolutionary phase, which is called preheating stage, provides an explosive particle production and must be discussed separately from the perturbative decay of inflaton. There are many works about the preheating stage based on analytical investigations as well as on numerical studies . The important feature with the existence of preheating stage is that the maximal value of produced fluctuation can be so large that it would result in a non-thermal phase transition and make baryogenesis at the GUT scale possible , although the baryogenesis might be important in much lower energy scale, i.e. the electro-weak scale .

Physical Review D, 1999

In higher-curvature inflation models (R + αnR n ), we study a parametric preheating of a scalar field χ coupled non-minimally to a spacetime curvature R (ξRχ 2 ). In the case of R 2 -inflation model, efficient preheating becomes possible for rather small values of ξ, i.e. |ξ| < ∼ several. Although the maximal fluctuation χ 2 max ≈ 2×10 17 GeV for ξ ≈ −4 is almost the same as the chaotic inflation model with a non-minimally coupled χ field, the growth rate of the fluctuation becomes much larger and efficient preheating is realized. We also investigate preheating for R 4 model and find that the maximal fluctuation is

Physical Review D

Journal of Cosmology and Astroparticle Physics, 2020

At the end of inflation, the inflaton oscillates at the bottom of its potential and these oscillations trigger a parametric instability for scalar fluctuations with wavelength λ comprised in the instability band (3Hm) −1/2 < λ < H −1 , where H is the Hubble parameter and m the curvature of the potential at its minimum. This "metric preheating" instability, which proceeds in the narrow resonance regime, leads to various interesting phenomena such as early structure formation, production of gravitational waves and formation of primordial black holes. In this work we study its fate in the presence of interactions with additional degrees of freedom, in the form of perturbative decay of the inflaton into a perfect fluid. Indeed, in order to ensure a complete transition from inflation to the radiation-dominated era, metric preheating must be considered together with perturbative reheating. We find that the decay of the inflaton does not alter the instability structure until the fluid dominates the universe content. As an application, we discuss the impact of the inflaton decay on the production of primordial black holes from the instability. We stress the difference between scalar field and perfect fluid fluctuations and explain why usual results concerning the formation of primordial black holes from perfect fluid inhomogeneities cannot be used, clarifying some recent statements made in the literature.

Physical Review D, 1999

We study inflationary models in which the effective potential of the inflaton field does not have a minimum, but rather gradually decreases at large φ. In such models the inflaton field does not oscillate after inflation, and its effective mass becomes vanishingly small, so the standard theory of reheating based on the decay of the oscillating inflaton field does not apply. For a long time the only mechanism of reheating in such non-oscillatory (NO) models was based on gravitational particle production in an expanding universe. This mechanism is very inefficient. We will show that it may lead to cosmological problems associated with large isocurvature fluctuations and overproduction of dangerous relics such as gravitinos and moduli fields. We also note that the setting of initial conditions for the stage of reheating in these models should be reconsidered. All of these problems can be resolved in the context of the recently proposed scenario of instant preheating if there exists an interaction g 2 φ 2 χ 2 of the inflaton field φ with another scalar field χ. We show that the mechanism of instant preheating in NO models is much more efficient than the usual mechanism of gravitational particle production even if the coupling constant g 2 is extremely small, 10 −14 ≪ g 2 ≪ 1.

Phys Rev D, 1999

We study inflationary models in which the effective potential of the inflaton field does not have a minimum, but rather gradually decreases at large $\phi$. In such models the inflaton field does not oscillate after inflation, and its effective mass becomes vanishingly small, so the standard theory of reheating based on the decay of the oscillating inflaton field does not apply. For a long time the only mechanism of reheating in such non-oscillatory (NO) models was based on gravitational particle production in an expanding universe. This mechanism is very inefficient. We will show that it may lead to cosmological problems associated with large isocurvature fluctuations and overproduction of dangerous relics such as gravitinos and moduli fields. We also note that the setting of initial conditions for the stage of reheating in these models should be reconsidered. All of these problems can be resolved in the context of the recently proposed scenario of instant preheating if there exists an interaction ${g^2} \phi^2\chi^2$ of the inflaton field $\phi$ with another scalar field $\chi$. We show that the mechanism of instant preheating in NO models is much more efficient than the usual mechanism of gravitational particle production even if the coupling constant $g^2$ is extremely small, $10^{-14} \ll g^2 \ll 1$.

Physical Review D, 1997

We consider preheating in the theory 1 4 λφ 4 + 1 2 g 2 φ 2 χ 2 , where the classical oscillating inflaton field φ(t) decays into χ-particles and φ-particles. The parametric resonance which leads to particle production in this conformally invariant theory is described by the Lame equation. It significantly differs from the resonance in the theory with a quadratic potential. The structure of the resonance depends in a rather nontrivial way on the parameter g 2 /λ. We construct the stability/instability chart in this theory for arbitrary g 2 /λ. We give simple analytic solutions describing the resonance in the limiting cases g 2 /λ ≪ 1 and g 2 /λ ≫ 1, and in the theory with g 2 = 3λ, and with g 2 = λ. From the point of view of parametric resonance for χ, the theories with g 2 = 3λ and with g 2 = λ have the same structure, respectively, as the theory 1 4 λφ 4 , and the theory λ 4N (φ 2 i) 2 of an N-component scalar field φi in the limit N → ∞. We show that in some of the conformally invariant theories such as the simplest model 1 4 λφ 4 , the resonance can be terminated by the backreaction of produced particles long before χ 2 or φ 2 become of the order φ 2. We analyze the changes in the theory of reheating in this model which appear if the inflaton field has a small mass.

Journal of Cosmology and Astroparticle Physics, 2008

We study preheating in theories where the inflaton couples derivatively to scalar and gauge fields. Such couplings may dominate in natural models of inflation, in which the flatness of the inflaton potential is related to an approximate shift symmetry of the inflaton. We compare our results with previously studied models with non-derivative couplings. For sufficiently heavy scalar matter, parametric resonance is ineffective in reheating the universe, because the couplings of the inflaton to matter are very weak. If scalar matter fields are light, derivative couplings lead to a mild longwavelength instability that drives matter fields to non-zero expectation values. In this case however, long-wavelength fluctuations of the light scalar are produced during inflation, leading to a host of cosmological problems. In contrast, axion-like couplings of the inflaton to a gauge field do not lead to production of long-wavelength fluctuations during inflation. However, again because of the weakness of the couplings to the inflaton, parametric resonance is not effective in producing gauge field quanta.

Physical Review D, 2015

In this paper we explored in detail a phenomenological model of modified single field natural inflation in light of recent cosmological experiments, BICEP2. Our main goal is to construct an inflationary model which not only predicts the important cosmological quantities such as (n s , r) compatible with experimental observation, but also is consistent with the low energy effective theory framework. Therefore, all the fundamental scale apart from M p and quantities of our interest should be within the sub-Planckian region. In order to achieve our goal we modify the usual single field natural inflationary model by a specific form of higher derivative kinetic term called kinetic gravity braiding (KGB). One of our guiding principles to construct such a model is the constant shift symmetry of the axion. We have chosen the form of the KGB term in such a way that it predicts the required value of n s ≃ 0.96 and a large tensor to scalar ratio r > 0.1. Importantly for a wide range of parameter space our model has sub-Planckian axion decay constant f and the scale of inflation Λ. However, the reheating after the end of inflation limits the value of f so that we are unable to get f to be significantly lower than M p. Furthermore, we find sub-Planckian field excursion for the axion field ∆φ ≃ f for the sufficient number of e-folding N 50. We also discussed in detail about the natural preheating mechanism in our model based on the recently proposed Chern-Simon coupling. We found this gravity mediated preheating is very difficult to achieve in our model. With our general analytic argument, we also would like to emphasize that Chern-Simons mediated preheating is very unlikely to happen in any slow roll inflationary model.

1998

One of the fundamental problems of modern cosmology is to explain the origin of all the matter and radiation in the Universe today. The inflationary model predicts that the oscillations of the scalar field at the end of inflation will convert the coherent energy density of the inflaton into a large number of particles, responsible for the present entropy of the Universe. The transition from the inflationary era to the radiation era was originally called reheating, and we now understand that it may consist of three different stages: preheating, in which the homogeneous inflaton field decays coherently into bosonic waves (scalars and/or vectors) with large occupation numbers; backreaction and rescattering, in which different energy bands get mixed; and finally decoherence and thermalization, in which those waves break up into particles that thermalize and acquire a black body spectrum at a certain temperature. These three stages are non-perturbative, non-linear and out of equilibrium, and we are just beginning to understand them. In this talk I will concentrate on the preheating part, putting emphasis on the differences between preheating in chaotic and in hybrid inflation.