Inflationary Scenario Research Articles

Post-Inflationary Production of Dark Matter after Inflection Point Slow Roll Inflation

We explore a feasible model that combines near-inflection point small-field slow roll inflationary scenario driven by single scalar inflaton with the production of non-thermal vector-like fermionic dark matter, χ, during the reheating era. For the inflationary scenario, we consider two separate polynomial forms of the potential; one is symmetric about the origin, and the other is not. We fix the coefficients of the potentials satisfying current Planck-Bicep data. We calculate the permissible range of yχ and mχ for the production of enough dark matter to explain the total Cold Dark Matter (CDM) mass density of the present universe while satisfying Cosmic Background Radiation (CMBR) measurements and other cosmological bounds.

Observational Imprints of Enhanced Scalar Power on Small Scales in Ultra Slow Roll Inflation and Associated Non-Gaussianities

The discovery of gravitational waves from merging binary black holes has generated considerable interest in examining whether these black holes could have a primordial origin. If a significant number of black holes have to be produced in the early universe, the primordial scalar power spectrum should have an enhanced amplitude on small scales, when compared to the COBE normalized values on the large scales that is strongly constrained by the anisotropies in the cosmic microwave background. In the inflationary scenario driven by a single, canonical scalar field, such power spectra can be achieved in models that permit a brief period of ultra slow roll inflation during which the first slow roll parameter decreases exponentially. In this review, we shall consider a handful of such inflationary models as well as a reconstructed scenario and examine the extent of formation of primordial black holes and the generation of secondary gravitational waves in these cases. We shall also discuss the strength and shape of the scalar bispectrum and the associated non-Gaussianity parameter that arise in such situations. We shall conclude with an outlook wherein we discuss the wider implications of the increased strengths of the non-Gaussianities on smaller scales.

Some aspects of inflationary scenario in the modified f(𝕋,𝒯 ) gravity

Inflationary cosmology was the subject of an investigation in the [Formula: see text] gravity context, for which [Formula: see text] stands for the torsion scalar while [Formula: see text] is the trace of the energy–momentum tensor using three different class of inflation potentials well known in the literature. In order to find the range of geometry-matter coupling parameter to describe cosmological inflation scenario, we determined the slow-roll parameters and predict the scalar spectral index [Formula: see text], the tensor to scalar ratio [Formula: see text] and tensor spectral index [Formula: see text] in function in inflation potential parameters. The results show that the range of geometry-matter coupling parameter found is in agreement with the PLANCK 2018 data and WMAP data.

Alternative approach to the Starobinsky model for inflation scenarios

The $R+{R}^{2}$ model of gravity with the corresponding shallow potential in the Einstein frame is consistent with the observations. Recently, many efforts have been made to generalize the $R+{R}^{2}$ (Starobinsky) model of inflation or use other shallow potentials to construct a model for the early Universe. We revise the question about the shallow potential. We propose a model in which the Starobinsky model can emerge through a dynamical mechanism. We show that the absence of ghost modes results to constraints on the parameters of the Starobinsky model. We obtain the scalar spectral index and the tensor-to-scalar ratio of the extended model and study the three-point correlation function of the curvature perturbation to estimate the primordial non-Gaussianities of the proposed model.

Constant-roll inflation from non-commutative geometry viewpoint

In this paper, we consider an inflation scenario in which the inflation roll rate, defined by [Formula: see text] is supposed to be constant and study constant-roll inflation by a scalar field with minimal coupling to gravity in the presence of non-commutative (NC) parameters. For this purpose, we use the deformation approach and obtain the corresponding Lagrangian to the model by employing new variables. Then, we find exact solutions for the inflation potential, which include power-law, quadratic hilltop, and natural inflation. Further, we discuss the effect of parameters on the inflation model in NC space.

The inflated Chern-Simons number in spectator chromo-natural inflation

The chromo-natural inflation (CNI) scenario predicts a potentially detectable chiral gravitational wave signal, generated by a Chern-Simons coupling between a rolling scalar axion field and an SU(2) gauge field with an isotropy-preserving classical background during inflation. However, the generation of this signal requires a very large integer Chern-Simons level, which can be challenging to explain or embed in a UV-complete model. We show that this challenge persists in the phenomenologically viable spectator field CNI (S-CNI) model. Furthermore, we show that a clockwork scenario giving rise to a large integer as a product of small integers can never produce a Chern-Simons level large enough to have successful S-CNI phenomenology. We briefly discuss other constraints on the model, both in effective field theory based on partial-wave unitarity bounds and in quantum gravity based on the Weak Gravity Conjecture, which may be relevant for further explorations of alternative UV completions.

Inflationary flavor oscillations and the cosmic spectroscopy

Inflationary scenarios motivated by high-energy physics generically contain a plethora of degrees of freedom beyond the primordial curvature perturbation. The latter interacts in a simple way with what we name "inflationary flavor eigenstates", which differ, in general, from freely propagating "mass eigenstates". We show that the mixing between these misaligned states results in new striking behaviors in the squeezed limit of the curvature perturbation three-point function, depending not only on the mass spectrum but also on the "mixing angles" of the theory. These results bring about a new perspective on the cosmological collider program: contrary to a widespread belief, the primordial signal needs not be dominated by the lightest extra degree of freedom. Instead, we show that it may display either modulated oscillations, a broken power law, or a transition from oscillations to a power law, thus offering a detailed cosmic spectroscopy of the particle content of inflation.

Swampland criteria of inflationary scalar field models with well-known potentials

We explore the swampland conjectures of quintessence and tachyon scalar field models in [Formula: see text] and Einstein gravities, respectively. In [Formula: see text] gravity, we consider cold and warm (by assuming generalized dissipative coefficient) inflationary scenarios and develop constraints on de-Sitter conjectures through Bekenstein entropy relation. In usual inflation, the de-Sitter conjecture constraint becomes constant (in terms of models constant parameters) which can be easily analyzed for its validity (i.e., [Formula: see text]). However, in warm inflation, we analyze the de-Sitter conjecture constraint through [Formula: see text], i.e., if [Formula: see text] then [Formula: see text] and hence we can obtain the required result. For evaluating this condition, we choose three well-known potentials such as monomial chaotic, hilltop and generalized exponential. It is observed that the condition [Formula: see text] satisfied for all three potentials in both regimes of dissipative coefficient for specific choice of constants. We also obtain satisfactory results of de-Sitter conjecture for tachyon and polytropic (with quintessence scalar field) in general relativity. We investigate the consistency of assumed potentials through inflationary parameters [Formula: see text] and [Formula: see text] comparing with Planck’s observational data 2018 and found them compatible with the recent observations.

Constraining cosmic inflation with observations: Prospects for 2030

ABSTRACT The ability to test and constrain theories of cosmic inflation will advance substantially over the next decade. Key data sources include cosmic microwave background (CMB) measurements and observations of the distribution of matter at low-redshift from optical, near-infrared, and 21-cm intensity surveys. A positive detection of a CMB B-mode consistent with a primordial stochastic gravitational wave background (SGWB) is widely viewed as a smoking gun for an inflationary phase. Still, a null result does not exclude inflation. However, in a significant class of inflationary scenarios, a low SGWB amplitude is correlated with a more significant running, αs, in the primordial density perturbations than is seen with the simplest inflationary potentials. With this motivation, we forecast the precision with which the spectral index ns and αs can be constrained by currently envisaged observations, including CMB (Simons Observatory, CMB-S4 and LiteBIRD), optical/near infra-red (DESI and SPHEREx), and 21-cm intensity mapping (Tianlai and CHIME) surveys. We identify optimal combinations of data sets for constraining the running and show that they may yield additional and informative constraints on the overall inflationary parameter space if the SGWB remains undetected.

Nearly Forgotten Cosmological Concept of E. B. Gliner

E. B. Gliner started his scientific career in 1963 at the age of 40. In 1965, when the existence of the cosmological constant λ seemed unnecessary to most cosmologists, he renewed interest in the problem by emphasizing a material interpretation of de Sitter space (i.e., the space curved in the presence of λ). According to that interpretation, the curvature is produced by a cosmological vacuum (now identified as dark energy of the universe). In 1970, Gliner proposed a description of exponential expansion (or contraction) of the universe at the early (or late) evolution stage dominated by cosmological vacuum. In 1975, Gliner (with I. G. Dyminikova) suggested a model of the early universe free of Big Bang singularity, and developed a scenario of nonsingular Friedmann cosmology. Many of these findings were used in the modern inflation scenarios of the universe, first proposed by A. A. Starobinsky (1979) and A. Guth (1981) and greatly multiplied later. However, these inflation scenarios differ from the scenario of Gliner and Dymnikova, and Gliner’s contribution to cosmology is nearly forgotten. The history and the essence of this contribution are outlined, as well the difference from the inflation theories.

Ultraviolet unitarity violations in non-minimally coupled scalar-Starobinsky inflation

We perform the calculation for tree-level ultraviolet unitarity violation scales for scalar-R 2 inflation models by including an additional R 2|Φ|2-type term. Due to certain constraints, we resort to the Einstein frame for our calculations, where we separate our analysis between metric and Palatini formulations. We follow recent works in this line that debunk the naive predictions for unitarity violations in Higgs' inflation models to determine how to accurately estimate the behaviour of scattering amplitudes in the UV limit. Later, we work out different cases by assuming potentials corresponding to known inflation scenarios so we could predict the range of coupling parameters for which the theories would remain unitary up to the Planckian regime. We also try to find the behaviour of the scattering amplitudes for these theories during the transition from inflationary to reheating epoch.

Trend inflation: Estimates for the Russian economy

The paper estimates the trajectory of trend inflation for Russia. A discussion of inflation measures used in macroeconomic models is presented, as well as the analysis of theoretical and empirical models that include a trend inflation indicator for monetary policy analysis. The paper also provides an overview of the use of trend inflation by monetary authorities of developed countries and emerging markets. Based on the methodology for assessing trend inflation with the help of models of unobservable components, the Kalman filter and including structural factors, the trajectory of trend inflation for the Russian economy from the beginning of 2001 to the end of 2021 is obtained. In addition, the paper provides a historical decomposition of cyclical inflation into structural shocks, as well as the decomposition of the variance of its forecast error into the considered shocks for 24 months in advance. The results of the econometric analysis testify in favor of a gradual decrease in the trend inflation rate to 4% per year after the 2015 crisis and further stabilization at this level. The situation in 2022 can be analyzed by analogy with the period of 2014—2015, one can expect a similar scenario for trend and actual inflation to return to pre-crisis levels in 2022 within one year (by March 2023).

From inflation to black hole mergers and back again: Gravitational-wave data-driven constraints on inflationary scenarios with a first-principle model of primordial black holes across the QCD epoch

Recent population studies have searched for a subpopulation of primordial black holes (PBHs) in the gravitational-wave (GW) events so far detected by LIGO/Virgo/KAGRA (LVK), in most cases adopting a phenomenological PBH mass distribution. When deriving such population from first principles in the standard scenario, however, the equation of state of the Universe at the time of PBH formation may strongly affect the PBH abundance and mass distribution, which ultimately depend on the power spectrum of cosmological perturbations. Here we improve on previous population studies on several aspects: (i) we adopt state-of-the-art PBH formation models describing the collapse of cosmological perturbations across the QCD epoch; (ii) we perform the first Bayesian multi-population inference on GW data including PBHs and directly using power spectrum parameters instead of phenomenological distributions; (iii) we critically confront the PBH scenario with LVK phenomenological models describing the GWTC-3 catalog both in the neutron-star and in the BH mass ranges, also considering PBHs as subpopulation of the total events. Our results confirm that LVK observations prevent the majority of the dark matter to be in the form of stellar mass PBHs. We find that the best fit PBH model can comprise a small fraction of the total events, in particular it can naturally explain events in the mass gaps. If the lower mass-gap event GW190814 is interpreted as a PBH binary, we predict that LVK should detect up to a few subsolar mergers and one to $\approx 30$ lower mass gap events during the upcoming O4 and O5 runs. Finally, mapping back the best-fit power spectrum into an ultra slow-roll inflationary scenario, we show that the latter predicts detectable PBH mergers in the LVK band, a stochastic GW background detectable by current and future instruments, and may include the entirety of dark matter in asteroid-mass PBHs.

Warm deformed R2 inflation

In this work, we study warm inflationary scenario based on a deformation of R2 gravity. We start considering Rp and assume p=2(1+δ) with δ≪1 so that we simply obtain warm R2 inflation when setting δ=0. We then derive the potential in the Einstein frame and consider a dissipation parameter of the form Γ=C1T with C1 being a coupling parameter. We focus only on the strong regime of which the interaction between inflaton and radiation fluid has been taken into account. We also consider a detailed analysis of the background dynamics, considering the evolution of the relevant quantities. We compute inflationary observables and constrain the parameters of our model using latest observational data reported by Planck. From our analysis, we discover that with proper choices of parameters the derived ns and r are in good agreement with the Planck 2018 observational constraints. Particularly, we constrain the potential scale U0 of the models.

Observational constraints on the interacting dark energy — Dark matter (IDM) cosmological models

Particle creation (or annihilation) mechanisms, described by either quantum field theoretical models, or by the thermodynamics of irreversible processes, play an important role in the evolution of the early Universe, like, for example, in the warm inflationary scenario. Following a similar approach, based on the thermodynamics of open systems, in the present work we investigate the consequences of the interaction, decay, and particle generation in a many-component Universe, containing dark energy, dark matter, radiation, and ordinary matter, respectively. In this model, due to the interaction between these components, and of the corresponding thermodynamical properties, the conservation equations of different cosmological constituents are not satisfied individually. We introduce a thermodynamic description of the Universe, in which two novel physical aspects, the particle number balance equations, and the creation pressures, are considered, thus making the cosmological evolution equations thermodynamically consistent. To constrain the free parameters of the model several observational data sets are employed, including the Planck data sets, Riess 2020, BAO, as well as Pantheon data. By using a scaling ansatz for the dark matter to dark energy ratio, and by imposing constraints from Planck+Riess 2020 data, this model predicts an acceptable value for the Hubble parameter, and thus it may provide a solution to the so-called Hubble tension problem, much debated recently.

Large field polynomial inflation: parameter space, predictions and (double) eternal nature

Simple monomial inflationary scenarios have been ruled out by recent observations. In this work we revisit the next simplest scenario, a single-field model where the scalar potential is a polynomial of degree four which features a concave “almost” saddle point. We focus on trans-Planckian field values. We reparametrize the potential, which greatly simplifies the procedure for finding acceptbale model parameters. This allows for the first comprehensive scan of parameter space consistent with recent Planck and BICEP/Keck 2018 measurements. Even for trans-Planckian field values the tensor-to-scalar ratio r can be as small as \U0001d4aa(10-8), but the model can also saturate the current upper bound. In contrast to the small-field version of this model, radiative stability does not lead to strong constraints on the parameters of the inflaton potential. For very large field values the potential can be approximated by the quartic term; as well known, this allows eternal inflation even for field energy well below the reduced Planck mass M Pl, with Hubble parameter H ∼ 10-2 M Pl. More interestingly, we find a region of parameter space that even supports two phases of eternal inflation. The second epoch only occurs if the slope at the would-be saddle point is very small, and has H ∼ 10-5 M Pl; it can only be realized if r ∼ 10-2, within the sensitivity range of next-generation CMB observations.

Cosmic Evolution of the Logarithmic f(R) Model and the dS Swampland Conjecture

In this paper, we study the inflationary scenario in logarithmic f(R) gravity, where the rate of inflation roll is constant. On the other hand, our gravitational f(R) model is a polynomial plus a logarithmic term. We take advantage of constant-roll conditions and investigate the cosmic evolution of the logarithmic f(R) gravity. We present a numerical and a graphical study using the model parameters. Additionally, we obtain the corresponding potential by using the constant-roll condition. We obtain the exact value of the potential satisfying the constant-roll conditions. Next, we challenge it with refined swampland conjecture with respect to the Planck data. Finally, we compare our results with the latest observable data.

K-Essence Inflation Evading Swampland Conjectures and Inflationary Parameters

In this paper, we study the inflationary scenario in the realm of k-essence model and swampland conjectures. Taking into account three models of Chaplygin gas, such as generalized, modified, and generalized cosmic Chaplygin gas models, we discuss the equation of state (EoS) parameter ω, slow roll parameters (ϵ(ϕ),η(ϕ)), curvature perturbation (Ps), tensor to scalar ratio (r), and scalar spectral index (ns). As regards the k-essence model, the coupling function as a function of scalar field L(ϕ) is used. We investigate the swampland conjecture and then find the value of ζ(ϕ), i.e., bound of second conjecture for these three models by unifying swampland conjecture and k-essence. We plot the EoS parameter ω, inflationary parameters plane r−ns and bound of swampland conjecture ζ(ϕ)−ϕ, which determine that the values of ω<−1 for each model, r, are r<0.0094,r≤0.0065,r≤0.0067, and ranges for ns are [0.934,0.999],[0.9,0.999],[0.9,0.992] for generalized, modified, and generalized cosmic Chaplygin gas models, respectively, and compare their compatibility with the Planck data from 2018. Furthermore, we determine the bound for swampland conjecture as ζ(ϕ)≤0.992,ζ(ϕ)≤0.964,ζ(ϕ)≤0.964 for generalized, modified and generalized cosmic Chaplygin gas models, respectively.

Creation field cosmological models for dust distribution and time-dependent cosmological term (Λ) in Bianchi type II space-time

In this paper, we present solution of Einstein field equations which admit dust distribution and negative energy massless scalar field as a source with cosmological term ([Formula: see text]) in the frame work of Bianchi type II space-time. The models satisfy conservation equation and creation field increases with time satisfying the result as investigated by Hoyle and Narlikar [A new theory of gravitation, Proc. Roy. Soc. A 282 (1964) 191]. The deceleration parameter ([Formula: see text]) for the model (22) shows a transition from decelerating to accelerating regime with creation. A comparison with other cosmological models shows a transition from decelerating to accelerating regime with and without creation is mentioned. The present model is free from singularity, particle horizon and provides a natural explanation for inflationary scenario and isotropization. These features make the creation field cosmological models theoretically superior to the Big Bang models. Creation field and Einstein field equation are derived using principle of least action and the Lagrangian formulation of variable cosmological term is derived as mentioned by Moffat [Lagrangian formulation of a solution to the cosmological constant problem (1996), arXiv:astro-ph/9608202v1]. The current creation rate with other physical consequences is also discussed. For illustrative purposes, evolutionary behaviors of some cosmological parameters are shown graphically. In the figures, the cosmic time [Formula: see text] is given in gravitational units assuming the velocity of light [Formula: see text]. This [Formula: see text] and [Formula: see text]. Therefore, by multiplying cosmic time [Formula: see text] by (light years)−1, we obtain the coordinate time in years.

Constraint on the Higgs-Dilaton Potential via Warm Inflation in Two-Time Physics

Within the S P 2 , R symmetry, the two-time model (2T model) has six dimensions with two dimensions of time and the dilaton field that can be identified as inflaton in a warm inflation scenario with potential of the form ~ ϕ 4 . From that consideration, we derive the range of parameters for the Higgs-Dilaton potential, the coupling constant between Higgs and Dilaton ( α ) is larger than 0.0053 and the mass of Dilaton is smaller than 1 0 − 7 GeV. Therefore, the 2T model indirectly suggests that extra dimension can also be a source of inflation.