Chaotic Inflation Model Research Articles

Formula omitted]- inflation: Sourced by energy–momentum squared gravity

In this paper, we examine chaotic inflation within the context of the energy–momentum squared gravity (EMSG) focusing on the energy–momentum powered gravity (EMPG) that incorporates the functional f(T2)∝(T2)β in the Einstein–Hilbert action, in which β is a constant and T2≡TμνTμν where Tμν is the energy–momentum tensor, which we consider to represent a single scalar field with a power-law potential. We also demonstrate that the presence of EMSG terms allows the single-field monomial chaotic inflationary models to fall within current observational constraints, which are otherwise disfavored by Planck and BICEP/Keck findings. We show that the use of a non-canonical Lagrangian with chaotic potential in EMSG can lead to significantly larger values of the non-Gaussianity parameter, fNlequi whereas EMSG framework with canonical Lagrangian gives rise to results similar to those of the standard single-field model.

Primordial gravitational waves by chaotic potential with a sharp step

We calculate the primordial gravitational wave spectrum observed today, Ω0gw(f) produced by a chaotic inflationary model featuring a step in its potential. Considering an inflaton field, slowly rolling down the potential, we analyze the scalar and tensor power spectra for the step potential model and found oscillatory density fluctuations within a specific range of wavenumbers around the feature. Localized small anomalies are observed in the tensor power spectrum also. We estimate the observational parameters, including the scalar spectral index (ns), tensor tilt (nt) and tensor-to-scalar ratio (r), which are found to be consistent with Planck satellite results. Additionally, by employing the relation between Ω0gw(f) and r, we determine the effective equation of state parameter wˆ(f) at the end of inflation. Evolution of wˆ(f) from 0.2 to 0.33, followed by constancy is obtained in the ntˆ(f)−wˆ(f) plot. This evolution of wˆ(f) is attributed to the reheating process, which is crucial for transitioning from the inflationary phase to the subsequent radiation-dominated era.

Non-minimally assisted chaotic inflation

Conventional wisdom says that a chaotic inflation model with a power-law potential is ruled out by the recent Planck-BICEP/Keck results. We find, however, that the model can be assisted by a non-minimally coupled scalar field and still provides a successful inflation. Considering a power-law chaotic inflation model of the type V ∼ φn with n = {2, 4/3, 1, 2/3, 1/3}, we show that n = 1/3 (n = {2/3, 1/3}) may be revived with the help of the quadratic (quartic) non-minimal coupling of the assistant field to gravity.

Validity of semiclassical limit to quantum gravity in two-mode oscillating quantized massive scalar field quantum cosmology

Semiclassical Einstein equations are used to describe the interaction of the back-reaction of the classical gravitational field with quantum matter fields in semiclassical gravity. We in our previous studies have made use of the semiclassical approximation to demonstrate the phenomenon of particle production, often called preheating/reheating of the universe, which occurs after the inflationary epoch during the oscillatory phase of two-mode quantized scalar field of chaotic inflationary model. During this oscillatory phase, back-reaction effects from the created particles, on account of the quantum nature of the states considered, could be significant and one might be concerned about the validity of the semiclassical approximation in these two-mode quantum optical states. The validity of the semiclassical approximation in these states is examined and it is presented how the magnitude of states parameter draws limit on the applicability and reliability of semiclassical theory of gravity. It is argued that semiclassical theory to gravity is a good approximation for states which are closer to coherent states i.e., with coherent parameters greater than unity and with squeezed parameter much smaller than unity.

Curvaton and quantum gravity effect on the tensor-to-scalar ratio of the chaotic inflation

The expected tensor-to-scalar ratio estimate of the upcoming CMB mission probe measurements may establish a lower value of the ratio than the currently obtained value. It can be described in terms of a single field chaotic inflation model along with the curvaton or quantum gravity or their combined effect. Consequently, the role of quantum gravity or curvaton in the dynamics of the early universe may not be ruled out. The curvaton scenario and quantum gravity effect can be tested experimentally. The upcoming CMB missions can validate the curvaton scenario and quantum gravity experimentally.

Unified emergence of energy scales and cosmic inflation

In the quest for unification of the Standard Model with gravity, classical scale invariance can be utilized to dynamically generate the Planck mass MPl. However, the relation of Planck scale physics to the scale of electroweak symmetry breaking μH requires further explanation. In this paper, we propose a model that uses the spontaneous breaking of scale invariance in the scalar sector as a unified origin for dynamical generation of both scales. Using the Gildener-Weinberg approximation, only one scalar acquires a vacuum expectation value of υS ∼ (1016−17) GeV, thus radiatively generating {M}_{mathrm{P}1}approx {beta}_S^{1/2}{upsilon}_S and μH via the neutrino option with right handed neutrino masses mN = yMυS ∼ 107 GeV. Consequently, active SM neutrinos are given a mass with the inclusion of a type-I seesaw mechanism. Furthermore, we adopt an unbroken Z2 symmetry and a Z2-odd set of right-handed Majorana neutrinos χ that do not take part in the neutrino option and are able to produce the correct dark matter relic abundance (dominantly) via inflaton decay. The model also describes cosmic inflation and the inflationary CMB observables are predicted to interpolate between those of R2 and linear chaotic inflationary model and are thus well within the strongest experimental constraints.

Favored Inflationary Models by Scalar Field Condensate Baryogenesis

We calculate the baryon asymmetry value generated in the Scalar Field Condensate (SCF) baryogenesis model obtained in several inflationary scenarios and different reheating models. We provide analysis of the baryon asymmetry value obtained for more than 70 sets of parameters of the SCF model and the following inflationary scenarios, namely: new inflation, chaotic inflation, Starobinsky inflation, MSSM inflation, quintessential inflation. We considered both cases of efficient thermalization after inflation and delayed thermalization. We have found that the SFC baryogenesis model produces baryon asymmetry orders of magnitude bigger than the observed one for the following inflationary models: new inflation, new inflation model by Shafi and Vilenkin, MSSM inflation, chaotic inflation with high reheating temperature and the simplest Shafi–Vilenkin chaotic inflationary model. Strong diluting mechanisms are needed for these models to reduce the resultant baryon excess at low energies to its observational value today. We have found that a successful generation of the observed baryon asymmetry is possible by the SCF baryogenesis model in Modified Starobinsky inflation, chaotic inflation with low reheating temperature, chaotic inflation in SUGRA, and Quintessential inflation.

Quantum fluctuations and cosmological particle creation from oscillating massive scalar field in two-mode quantum optical states

In this paper, by the use of entangled and nonentangled coherent and squeezed state formalism of two-mode nonclassical states, we studied the chaotic inflationary model of a massive scalar field with quadratic potential in the semiclassical gravity, derived from canonical quantum gravity. It was found that the semiclassical quantum gravity leads to the same power-law expansion of the universe as that of the matter-dominated era [Formula: see text] in an oscillatory phase of the scalar field in all the nonclassical quantum states considered. The coherently oscillating scalar field in the expanding universe suffers from the phenomenon of particle creation which restricts the duration of stable coherent oscillations of the scalar field dependent on the parameters of the states considered and affect in a certain way the abundant particle production owing to the parametric resonance of bosonic fields coupled to this coherently oscillating scalar field.

Observable quantum loop effects in the sky

Expanding on [1], we analyze in detail the single field chaotic inflationary models plus a cosine modulation term, augmented by a light scalar field with inflaton dependent oscillatory mass term. We work out in detail the Feynman diagrams and compute one, two and in general estimate higher loop two and three point functions in the in-in formulation. We explicitly establish how the oscillatory mass term can amplify one-loop effects to dominate over the tree as well as the higher loop contributions. The power spectrum of curvature perturbations of this model is hence enhanced compared to the simple single field chaotic model. As a consequence, one can suppress the tensor to scalar ratio r and have a different expression for scalar spectral tilt and the running of the tilt, opening the way to reconcile chaotic models with convex potential and the Planck data. As in monodromy inflation models, we also have a cosine modulation in the spectral tilt. We also analyze the bispectrum, which can be dominated by the amplified one-loop effects, yielding a new shape in non-Gaussianity. We discuss the bounds on parameter space from all available CMB observables and possible implications for reheating.

Favoured Inflationary Models by SFC Baryogenesis

AbstractWe provide analysis of the baryon asymmetry generated in the Scalar Field Condensate (SFC) baryogenesis model obtained in new inflation, chaotic inflation, Starobinsky inflation, MSSM inflation, quintessential inflation, considering both cases of efficient thermalization after inflation and also delayed thermalization. We have found that baryon asymmetry generated in SFC baryogenesis model is considerably bigger than the observed one for the new inflation, new inflation model by Shafi and Vilenkin, MSSM inflation, chaotic inflation with high reheating temperature and the simplest Shafi-Vilenkin chaotic inflationary model. Therefore, strong diluting mechanisms are needed to reduce the baryon excess to its observational value today for these models. We have shown that for the SFC baryogenesis model a successful generation of the observed baryon asymmetry is possible in Modified Starobinsky inflation, chaotic inflation with low reheating temperature, chaotic inflation in SUGRA and quintessential inflationary model.

Chaotic inflation with four-form couplings

We consider chaotic inflation models with a pseudo-scalar field containing the general couplings to the four-form flux. The four-form mixing with the pseudo-scalar field induces a quadratic potential for inflaton while the coexisting four-form mixing with graviton generates a non-minimal gravity coupling for inflaton. The shift symmetry is respected by the derived inflaton couplings and it is broken spontaneously only by the fixed four-form flux. We discuss the success of inflationary predictions and robustness against higher order terms. Finally, the built-in reheating mechanism is also addressed.

Resonant reconciliation of convex-potential inflation models and the Planck data

We consider single field chaotic inflationary models plus a cosine modulation term, as in axion monodromy models, and augment it by a light scalar field with similar cosine coupling. We show the power spectrum of curvature perturbations of this model is dominated by the one-loop contribution to inflaton two-point function which is enhanced due to resonant interactions. This allows to disentangle the scale of scalar and tensor perturbations and hence to suppress the ratio of tensor-to-scalar power spectra and alters the expression of scalar spectral tilt from the simple chaotic models, thus opening the way to reconcile chaotic models with convex potential and the Planck data. As in monodromy inflation models, we also have a cosine modulation in spectral tilt. We mention that contribution of resonance effects on non-Gaussianty is small and it remains within the current bounds. Resonant production of light particles toward the end of inflation may set the stage for a successful reheating model.

Inflation with derivative self-interaction and coupling to gravity

We consider a subclass of Horndeski theories for studying cosmic inflation. In particular, we investigate models of inflation in which the derivative self-interaction of the scalar field and the non-minimal derivative coupling to gravity are present in the action and equally important during inflation. In order to control contributions of each term as well as to approach the single-term limit, we introduce a special relation between the derivative interaction and the coupling to gravity. By calculating observable quantities including the power spectra and spectral tilts of scalar and tensor perturbation modes, and the tensor-to-scalar ratio, we found that the tensor-to-scalar ratio is suppressed by a factor of (1+1/gamma ), where gamma reflects the strength of the derivative self-interaction of the inflaton field with respect to the derivative coupling gravity. We placed observational constraints on the chaotic and natural inflation models and showed that the models are consistent with the current observational data mainly due to the suppressed tensor-to-scalar ratio.

Numerical Study of Inflationary Preheating with Arbitrary Power-law Potential and a Realization of Curvaton Mechanism

Abstract During inflationary preheating, the energy stored in the inflaton field is rapidly converted into excitations of other entropy fields. This stage is characterized by exponential particle production due to parametric resonance and is notoriously difficult to analyze using analytic methods. We develop a detailed numerical simulation to investigate inflationary preheating when the potential of the inflaton is a power-law function with arbitrary power index. To achieve a successful graceful exit from a primordial inflationary phase to a smooth, oscillatory phase during preheating, we assume the inflaton potential reduces to a quadratic function in the infrared regime, which may be regarded as a mass term at low-energy scales. With this simplification, our numerical method may be applied to unconventional chaotic inflation models. To demonstrate its validity, we numerically analyze the preheating stage of axion-monodromy inflation, which is inspired by string theory. By performing perturbation analyses, our result shows that the power spectrum of primordial curvature perturbation can be dominated by fluctuations of entropy field rather than those of inflaton, which can be regarded as a particular realization of the curvaton mechanism through a preheating process.

Unitarity-safe models of non-minimal inflation in supergravity

We show that models of chaotic inflation based on the phi ^p potential and a linear non-minimal coupling to gravity, f_{{mathcal {R}}}=1+c_{{mathcal {R}}}phi , can be done consistent with data in the context of Supergravity, retaining the perturbative unitarity up to the Planck scale, if we employ logarithmic Kähler potentials with prefactors -p(1+n) or -p(n+1)-1, where -0.035lesssim nlesssim 0.007 for p=2 or -0.0145lesssim nlesssim 0.006 for p=4. Focusing, moreover, on a model employing a gauge non-singlet inflaton, we show that a solution to the mu problem of MSSM and baryogenesis via non-thermal leptogenesis can be also accommodated.

Reconstructing $f(R)$ gravity from the spectral index

Recent cosmological observations are in good agreement with the scalar spectral index $n_s$ with $n_s-1\simeq -2/N$, where $N$ is the number of e-foldings. In the previous work, the reconstruction of the inflaton potential for a given $n_s$ was studied, and it was found that for $n_s-1=-2/N$, the potential takes the form of either $\alpha$-attractor model or chaotic inflation model with $\phi^2$ to the leading order in the slow-roll approximation. Here we consider the reconstruction of $f(R)$ gravity model for a given $n_s$ both in the Einstein frame and in the Jordan frame. We find that for $n_s-1=-2/N$ (or more general $n_s-1=-p/N$), $f(R)$ is given parametrically and is found to asymptote to $R^2$ for large $R$. This behavior is generic as long as the scalar potential is of slow-roll type.

Sneutrinos as mixed inflaton and curvaton

We investigate a scenario where the supersymmetric partners of two right-handed neutrinos (sneutrinos) work as mixed inflaton and curvaton, motivated by the fact that the curvaton contribution to scalar perturbations can reduce the tensor-to-scalar ratio r so that chaotic inflation models with a quadratic potential are made consistent with the experimental bound on r. After confirming that the scenario evades the current bounds on r and the scalar perturbation spectral index ns, we make a prediction on the local non-Gaussianity in bispectrum, fNL, and one in trispectrum, τNL. Remarkably, since the sneutrino decay widths are determined by the neutrino Dirac Yukawa coupling, which can be estimated from the measured active neutrino mass differences in the seesaw model, our scenario has a strong predictive power about local non-Gaussianities, as they heavily depend on the inflaton and curvaton decay rates. Using this fact, we can constrain the sneutrino mass from the experimental bounds on ns, r and fNL.

Palatini side of inflationary attractors

We perform an analysis of models of chaotic inflation where the inflaton field $\phi$ is coupled non-minimally to gravity via $\xi \phi^n g^{\mu\nu}R_{\mu\nu}(\Gamma), n>0$. We focus on the Palatini theory of gravity, i.e. the case where the assumptions of the General Relativity are relaxed (that of the connection being the Levi-Civita one) and the gravitational degrees of freedom are encoded not only in the metric but also the connection $\Gamma$, which is treated as an independent variable. We show that in this case the famous attractor behaviour of simple non-minimally coupled models of inflation is lost. Therefore the attractors are not universal but their existence depends on the underlying theory of gravity in a subtle way. We discuss what this means for chaotic models and their observational consequences.

Study of some chaotic inflationary models in f ( R ) $f(R)$ gravity

In this paper, we discuss inflationary scenario via scalar field and fluid cosmology for anisotropic homogeneous universe model in $f(R)$ gravity. We consider an equation of state which corresponds to quasi-de Sitter expansion and investigate the effect of anisotropy parameter for different values of deviation parameter. We evaluate potential models like linear, quadratic and quartic which correspond to chaotic inflation. We construct the observational parameters for power-law model of $f(R)$ gravity and construct the graphical analysis of tensor-scalar ratio and spectral index which indicates consistency of these parameters with Planck 2015 data.

Evolution of the universe driven by a mass-dimension-one fermion field

This paper studies the evolution of the universe filled with a neutral mass-dimension-one fermionic field, sometimes called Elko. The numerical analysis of the coupled system of equations furnishes a scale factor growth and energy density evolution that correctly reproduce the inflationary phase of the universe. After that, assuming a mechanism of energy transference to ordinary matter, the initial conditions generated after inflation drives the radiation-dominated phase and also the subsequent dark-matter evolution, since the Elko field is a good dark-matter candidate. The energy density of the field at the end of inflation, at the end of the radiation phase and for the present time are in agreement with the standard model estimates. The analysis was performed with a potential containing a quadratic mass term plus a quartic self-interaction term, which follows naturally from the theory of mass-dimension-one fermions. Inflation occurs when the field makes a kind of transition around the Planck mass scale. The number of e-foldings during inflation was found to be strongly dependent on the initial conditions of the Elko field, as occurs in chaotic inflationary models. An upper limit to the Elko mass is estimated. A possible interpretation of the inflation as a consequence of a kind of Pauli exclusion principle is presented at the end.