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We study particle production at the end of inflation in kinetically driven G-inflation model and show that, in spite of the fact that there are no inflaton oscillations and hence no parametric resonance instabilities, the production of matter particles due to a coupling to the evolving inflaton field can be more efficient than pure gravitational Parker particle production.
Physical Review D, 2010
Inflation is studied in the context of induced gravity (IG) $\gamma \sigma^2 R$, where $R$ is the Ricci scalar, $\sigma$ a scalar field and $\gamma$ a dimensionless constant, and diverse symmetry-breaking potentials $V(\sigma)$ are considered. In particular we compared the predictions for Landau-Ginzburg (LG) and Coleman-Weinberg (CW) type potentials and their possible generalizations with the most recent data. We find that large field inflation generally leads to fewer constraints on the parameters and the shape of the potential whereas small field inflation is more problematic and, if viable, implies more constraints, in particular on the parameter $\gamma$. We also examined the reheating phase and obtained an accurate analytical solution for the dynamics of inflaton and the Hubble parameter by using a multiple scale analysis (MSA). The solutions were then used to study the average expansion of the Universe, the average equation of state for the scalar field and both the perturbative and resonant decays of the inflaton field.
Physical Review D, 1997
Reheating after inflation occurs due to particle production by the oscillating inflaton field. In this paper we briefly describe the perturbative approach to reheating, and then concentrate on effects beyond the perturbation theory. They are related to the stage of parametric resonance, which we called preheating. It may occur in an expanding universe if the initial amplitude of oscillations of the inflaton field is large enough. We investigate a simple model of a massive inflaton field φ coupled to another scalar field χ with the interaction term g 2 φ 2 χ 2. Parametric resonance in this model is very broad. It occurs in a very unusual stochastic manner, which is quite different from parametric resonance in the case when the expansion of the universe is neglected. Quantum fields interacting with the oscillating inflaton field experience a series of kicks which, because of the rapid expansion of the universe, occur with phases uncorrelated to each other. Despite the stochastic nature of the process, it leads to exponential growth of fluctuations of the field χ. We call this process stochastic resonance. We develop the theory of preheating taking into account the expansion of the universe and backreaction of produced particles, including the effects of rescattering. This investigation extends our previous study of reheating after inflation [1]. We show that the contribution of the produced particles to the effective potential V (φ) is proportional not to φ 2 , as is usually the case, but to |φ|. The process of preheating can be divided into several distinct stages. In the first stage the backreaction of created particles is not important. In the second stage backreaction increases the frequency of oscillations of the inflaton field, which makes the process even more efficient than before. Then the effects related to scattering of χ-particles on the oscillating inflaton field terminate the resonance. We calculate the number density of particles nχ produced during preheating and their quantum fluctuations χ 2 with all backreaction effects taken into account. This allows us to find the range of masses and coupling constants for which one can have efficient preheating. In particular, under certain conditions this process may produce particles with a mass much greater than the mass of the inflaton field.
Physics Letters B, 2009
Inflation is studied in the context of induced gravity (IG) γ σ 2 R, where R is the Ricci scalar, σ a scalar field and γ a dimensionless constant. We study in detail cosmological perturbations in IG and examine both a Landau-Ginzburg (LG) and a Coleman-Weinberg (CW) potential toy models for small field and large field (chaotic) inflation and find that small field inflationary models in IG are constrained to γ 3 × 10 −3 by WMAP 5-yrs data. Finally we describe the regime of coherent oscillations in induced gravity by an analytic approximation, showing how the homogeneous inflaton can decay in its short-scale fluctuations when it oscillates around a non-zero value σ 0 .
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 .
Journal of Cosmology and Astroparticle Physics, 2009
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.
Physical Review D
We propose a model for cosmic inflation which is based on an effective description of strongly interacting, nonsupersymmetric matter within the framework of dynamical abelian projection and centerization. The underlying gauge symmetry is assumed to be SU(N) with N≫1. Appealing to a thermodynamical treatment, the ground-state structure of the model is determined by a potential for the inflaton field (monopole condensate) which allows for nontrivially BPS saturated and thereby stable solutions. For T < MP this leads to an apparent decoupling of gravity from the inflaton dynamics. The ground state dynamics implies a heat capacity for the vacuum leading to inflation for temperatures comparable to the mass scale M of the potential. The dynamics has an attractor property. In contrast to the usual slow-roll paradigm we have m ≫ H during inflation. As a consequence, density perturbations generated from the inflaton are irrelevant for the formation of large-scale structure, and the model has to be supplemented with an inflaton independent mechanism for the generation of spatial curvature perturbations. Within a small fraction of the Hubble time inflation is terminated by a transition of the theory to its center symmetric phase. Due to the prevailing ZN symmetry relic vector bosons are stabilized and therefore potential originators of UHECR's beyond the GZK bound.
Physics Letters B, 2003
We discuss a model in which high energy brane corrections allow a single scalar field to describe inflation at early epochs and quintessence at late times. The reheating mechanism in the model originates from Born-Infeld matter whose energy density mimics cosmological constant at very early times and manifests itself as radiation subsequently. For most of the inflationary evolution the Born-Infeld matter remains subdominant to the the scalar field. Shortly before the end of inflation driven by the scalar field, the energy density of Born-Infeld matter starts scaling as radiation and drops by several orders of magnitudes at the epoch inflation ends. The problem of over production of gravity wave background in scenarios based upon reheating through gravitational particle production is successfully resolved by suitably fixing the initial value of radiation energy density at the end of inflation. No additional fine tuning of the parameters is required for a viable evolution.
1997
At the end of the inflationary stage of the early universe, profuse particle production leads to the reheating of the universe. Such explosive particle production is due to parametric amplification of quantum fluctuations for the unbroken symmetry case (appropriate for chaotic inflation), or spinodal instabilities in the broken symmetry phase(which is the case in new inflation). The self-consistent methods presented in these lectures are the only approaches, so far, that lead to reliable quantitative results on the reheating mechanism in the inflationary universe. They fully use the field theoretical Schwinger-Keldysh out of equilibrium method in a non-perturbative way. These approaches take into account the non-linear interaction between the quantum modes and exactly conserve energy (covariantly). Simplified analysis that do not include the full backreaction and do not conserve energy, result in unbound particle production and lead to quantitatively erroneous results. For spontaneously broken theories the issue of whether the symmetry may be restored or not by the quantum fluctuations is analyzed. The precise criterion for symmetry restoration is presented. The field dynamics is symmetric when the energy density in the initial state is larger than the top of the tree level potential. When the initial energy density is below the top of the tree level potential, the symmetry is broken.
2011
A gauge invariant combination of LLe sleptons within the Minimal Supersymmetric Standard Model is one of the few inflaton candidates that can naturally explain population of the observable sector and creation of matter after inflation. After the end of inflation, the inflaton oscillates coherently about the minimum of its potential, which is a point of enhanced gauged symmetry. This results in bursts of non-perturbative production of the gauge/gaugino and (s)lepton quanta. The subsequent decay of these quanta is very fast and leads to an extremely efficient transfer of the inflaton energy to (s)quarks via instant preheating. Around 20% of the inflaton energy density is drained during every inflaton oscillation. However, all of the Standard Model degrees of freedom (and their supersymmetric partners) do not thermalize immediately, since the large inflaton vacuum expectation value breaks the electroweak symmetry. After about 100 oscillations -albeit within one Hubble time -the amplitude of inflaton oscillations becomes sufficiently small, and all of the degrees of freedom will thermalize. This provides by far the most efficient reheating of the universe with the observed degrees of freedom.
General Relativity and Gravitation
I study a fresh inflationary model with a scalar field nonminimally coupled to gravity. An example is examined. I find that, as larger is the value of p (a ∼ t p), smaller (but larger in its absolute value) is the necessary value of the coupling ξ to the inflaton field fluctuations can satisfy a scale invariant power spectrum.
Physical Review D, 2008
The impact of particle production during inflation on the primordial curvature perturbation spectrum is investigated both analytically and numerically. We obtain an oscillatory behavior on small scales, while on large scales the spectrum is unaffected. The amplitude of the oscillations is proportional to the number of coupled fields, their mass, and the square of the coupling constant. The oscillations are due a discontinuity in the second time derivative of the inflaton, arising from a temporary violation of the slow-roll conditions. A similar effect on the power spectrum should be produced also in other inflationary models where the slow-roll conditions are temporarily violated.
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.
Physical Review D, 1998
Inflationary reheating via resonant production of non-minimally coupled scalar particles with only gravitational coupling is shown to be extremely strong, exhibiting a negative coupling instability for ξ < 0 and a wide resonance decay for ξ ≫ 1. Since non-minimal fields are generic after renormalization in curved spacetime, this offers a new paradigm in reheating -one which naturally allows for efficient production of the massive bosons needed for GUT baryogenesis. We also show that both vector and tensor fields are produced resonantly during reheating, extending the previously known correspondences between bosonic fields of different spin during preheating.
Il Nuovo Cimento B, 1996
Physical Review D, 2001
We estimate the production of gravitinos during and after the end of a period of warm inflation, a model in which radiation is produced continuously as the field rolls down the potential producing dissipation. We find that gravitino production is efficient for models in the strong dissipation regime, with the result that standard nucleosynthesis is disrupted unless the magnitude of the inflaton potential is very small. Combining this with the constraint from the thermal production of adiabatic density perturbations we find the dissipation rate must be extraordinarily strong, or that the potential is very flat.
Arxiv preprint hep-ph/ …, 1995
We consider the non-equilibrium evolution of the inflaton field coupled to both lighter scalars and fermions. The dissipational dynamics of this field is studied and found to be quite different than that believed in inflationary models. In particular, the damping time scale for the expectation value of the zero momentum mode of the inflaton can be much shorter than that given by the single particle decay rate when the inflaton amplitudes are large, as in chaotic inflation scenarios. We find that the reheating temperature may depart considerably from the usual estimates. 98.80.Cq, 11.15.Tk
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, $10^{-14} \ll g^2 \ll 1$.
2008
Whichever could be the real theory of gravitation, the corresponding low-energy effective lagrangian will probably contain higher derivative terms. In this work we study the general conditions on those terms in order to produce enough inflation to solve some of the problems of the standard Friedmann-Robertson-Walker cosmology in absence of any inflaton field. We apply our results to some particular scenarios where higher derivative terms appear in the effective lagrangian for gravity like those coming from graviton (two)-loops or integrating out ordinary matter (like the one present in the Standard Model).
Physical Review D, 2001
We propose a scenario for inflation based upon the braneworld picture, in which high-energy corrections to the Friedmann equation permit inflation to take place with potentials ordinarily too steep to sustain it. Inflation ends when the braneworld corrections begin to lose their dominance. Reheating may naturally be brought about via gravitational particle production, rather than the usual inflaton decay mechanism; the reheat temperature may be low enough to satisfy the gravitino bound and the Universe becomes radiation dominated early enough for nucleosynthesis. We illustrate the idea by considering steep exponential potentials, and show they can give satisfactory density perturbations (both amplitude and slope) and reheat successfully. The scalar field may survive to the present epoch without violating observational bounds, and could be invoked in the quintessential inflation scenario of Peebles and Vilenkin.
Physical Review D, 2006
We present a model which predicts inflation without the presence of inflaton fields, based on the ϵR 2 and Starobinsky models. It links the above models to the reheating epoch with conformally coupled massive particles created at the end of inflation. In the original Starobinsky ...
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