Inflationary Cosmological Models Research Articles

Bianchi Type-VIII Inflationary Cosmological Models with Flat Potential and Stiff perfect Fluid Distribution in General Relativity

The objective of this paper is to investigate the behaviour of Bianchi Type-VIII Inflationary Cosmological Models with Flat Potential for Stiff Fluid Distribution. To find the solution of thes models we consider that the expansion theta is proportional to the shear sigma, which leads to B = An and potential V (phi ) as a constant. The behaviour of these models from physical and geometrical aspects are also discussed.

Bianchi Type V Inflationary Cosmological Model with Bulk Viscosity in General Relativity

Bianchi Type V Inflationary Cosmological Model with Bulk Viscosity in General Relativity

Inflationary Cosmological Model of Bianchi Type II in General Relativity

Inflationary Cosmological Model of Bianchi Type II in General Relativity

Relic gravitational waves in verified inflationary models based on the generalized scalar–tensor gravity

In this work, we consider the models of cosmological inflation based on generalized scalar–tensor theories of gravity with quadratic connection between the Hubble parameter and coupling function. For such a class of the models, we discuss the correspondence between well-known versions of the scalar–tensor gravity theories and physically motivated potentials of a scalar field. It is shown that this class of models corresponds to the Planck observational constraints on the cosmological perturbation parameters for an arbitrary potential of a scalar field and arbitrary version of a scalar–tensor gravity theory. The spectrum of relict gravitational waves is analyzed, and the frequency range corresponding to maximal energy density is determined. The possibility of direct detection of the relic gravitational waves, predicted in such a class of models, by satellite and ground-based detectors is discussed as well.

Singularities in Inflationary Cosmological Models

Due to the accelerated expansion of the universe, the possibilities for the formation of singularities has changed from the classical Big Bang and Big Crunch singularities to include a number of new scenarios. In recent papers it has been shown that such singularities may appear in inflationary cosmological models with a fractional power scalar field potential. In this paper we enlarge the analysis of singularities in scalar field cosmological models by the use of generalised power expansions of their Hubble scalars and their scalar fields in order to describe all possible models leading to a singularity, finding other possible cases. Unless a negative scalar field potential is considered, all singularities are weak and of type IV.

Exploring the parameter space of modified supergravity for double inflation and primordial black hole formation

We study the parameter space of the effective (with two scalars) models of cosmological inflation and primordial black hole (PBH) formation in the modified (R + R 2) supergravity. Our models describe double inflation, whose first stage is driven by Starobinsky’s scalaron coming from the R 2 gravity, and whose second stage is driven by another scalar belonging to the supergravity multiplet. The ultra-slow-roll regime between the two stages leads a large peak (enhancement) in the power spectrum of scalar perturbations, which results in efficient PBH formation. Both inflation and PBH formation are generic in our models, while those PBH can account for a significant part or the whole of dark matter. Some of the earlier proposed models in the same class are in tension (over 3σ) with the observed value of the scalar tilt n s, so that we study more general models with more parameters, and investigate the dependence of the cosmological tilts (n s, r) and the scalar power spectrum enhancement upon the parameters. The PBH masses and their density fraction (as part of dark matter) are also calculated. A good agreement (between 2σ and 3σ) with the observed value of n s requires fine tuning of the parameters, and it is only realized in the so-called δ-models. Our models offer the (super)gravitational origin of inflation, PBH and dark matter together, and may be confirmed or falsified by future precision measurements of the cosmic microwave background radiation and PBH-induced gravitational waves.

The great emptiness at the beginning of the Universe

The great emptiness is a possible beginning of the Universe in the infinite past of physical time. For the epoch of great emptiness particles are extremely rare and effectively massless. Only expectation values of fields and average fluctuations characterize the lightlike vacuum of this empty Universe. The physical content of the early stages of standard inflationary cosmological models is the lightlike vacuum. Towards the beginning, the Universe is almost scale invariant. This is best seen by an appropriate choice of the metric field – the primordial flat frame – for which the beginning of a homogeneous metric is flat Minkowski space. We suggest that our observed inhomogeneous Universe can evolve from the lightlike vacuum in the infinite past, and therefore can have lasted eternally. Then no physical big bang singularity is present.

A semi-classical model of regular inflationary cosmology

Quantum-effective gravity must lead to a regularized cosmology and thereby by itself source and regulate the high energy inflaton fields required for an appropriate inflationary beginning of the Universe. Pursuing this premise, we involve in the generic code of extended theories of gravity in conceiving semi-classical imprinting of quantum effects into gravitation. Hence, we prescribe a general semi-classical procedure of constructing the regular, quantum-effective form of the spatially flat FLRW cosmology whereby two alternative classes of the admissible dynamics are distinguished. In this paper, we explore only the particular class holding a minimally inflationary de Sitter UV-phase. Curiously, the low energy phase of the newly modeled Universe recovers the conventional dynamics of loop quantum cosmology. However, unlike the loop quantum cosmology, the high energy phase of the newly conceived cosmology has no bounce, instead, has a regular whimpering emergence of the Universe replacing the Big Bang. Our analysis manifests that without needing any non-standard equation of state, ordinary matter admits an inflationary beginning of the Universe.

МУЛЬТИВЕРСУМ: ФІЛОСОФСЬКА РЕФЛЕКСІЯ НАД ТЕОРЕТИЧНИМИ ІДЕЯМИ ТА ЕМПІРИЧНИМИ ДАНИМИ

The cosmological conception of the Multiverse was formulated based on unitary gauge theories in the Physics of high energy. Theoretically expected, the quantum fluctuations of the original scalar field in a vacuum state and different variants of local symmetries breaking in the process of Early Universe expansion were the reasons for the cosmological idea of many possible worlds or Multiverse. Together with the inflationary cosmological model, these ideas successfully solved the problems of Big Bang theory with an explanation of observable quasi-Euclidean geometry in our world and isotropy and homogeneity of space on a mega-scale. New observational data, especially discovery of accelerative widening of space, so as the problem of dark matter and dark energy put for cosmology the new questions. These questions need to be philosophically comprehended. Professor Sergiy Krymsky offered an interesting understanding of the notion of "matter" in the situation of many worlds in the 80s. He considered each of the possible worlds as "matter, kept in its specificity", which existed in its own space and time with its set of elements, physical laws and constants. However, his considering the original vacuum state of scalar field as non-being is not satisfied because its heterogeneity defines further places for becoming of Galaxies. In this article, the author considers the ideas about the ontological status of the original state of the Early Universe in modern cosmological Multiverse theories and discusses the possible antinomies in these transcendental ideas and their difference from Kantian ones. Experience of solution the Kant’s antinomy in history of physics was taken into account. It was the second antinomy of discreetness / continuality. The solution was haven get in a way proposed by Kant, namely with empirical research and their theoretical explanations. Cosmological application of High Energy Physics gets it to transcendental ideas area, namely to the problem of our world becoming one of the possible worlds, just as a particular variant of first Kant's antinomy. However, formulation of antinomy connected with consideration of the ontological status of original state for becoming of our world has other categorical expressions than Kantian one. The front position belongs here to categories of possibility and actuality, which Kant did not include in the area of transcendental ideas, thinking that the contingency, connecting with possibility, must be changed by inevitable necessity in cognitive progress. On the contrary, contingency has the main place in modern cosmological scenarios, depending on multiple possibilities. So categories of possibility and actuality in the foundations of scientific theories need special attention. Now it touches upon at least two moments: the virtual particles as abstract objects of relativistic quantum theories and to the problem of understanding the ontological status of category "matter" in foundations of many world cosmology in the context of relations to categories "possibility", "actuality" and "reality".

Bianchi Type VI Inflationary Cosmological Model with Massive String Source in General Relativity

Bianchi Type VI Inflationary Cosmological Model with Massive String Source in General Relativity

Galaxies in Observations and Numerical Models

A comparison of the virial parameters of galaxies and galaxy clusters (radius, density, and entropy function) in a wide range of masses, $${{10}^{6}} \leqslant {{M}_{{{\text{vir}}}}}{\text{/}}{{M}_{ \odot }} \leqslant {{10}^{{14}}}$$ , shows that these parameters are correlated and depend on the virial mass of an object in a regular way. For the observed galaxies and galaxy clusters the available estimates of virial parameters are quite close to each other and the values of reduced virial density Gρ are concentrated in a shallow interval $$0.5 \leqslant {{G}_{\rho }}{\text{/}}\langle {{G}_{\rho }}\rangle \leqslant 2$$ around its mean value. This “virial” paradox sharpen when compared with simulations, in which the number of such objects is very small, and for the majority of dark matter halos these densities are ~50–100 times smaller. Our theoretical analysis shows possible reasons for this discrepancy of observations and simulations, pointing out its connection with the spectrum of cosmological perturbations. After some refinement, the considered data can be used to constrain models of cosmological inflation. A number of accompanying questions is discussed.

QUBIC: Observing the Polarized Microwave Sky over the Puna

QUBIC (Q&U Bolometric Interferometer for Cosmology) is an experiment designed to measure the polarization of the cosmic microwave background (CMB), the relic radiation from the Big- Bang. Detailed measurements of tiny temperature anisotropies in the CMB shaped our understanding of the early Universe. Accurate measurements of its polarization may reveal even earlier features, in particular the presence of gravitational waves with primordial origin. Such measurements can probe inflationary cosmological models, which postulate that quantum effects during an accelerated expansion at the earliest stages after the Big-Bang produced gravitational waves along with the density fluctuations that later seeded galaxy formation. QUBIC will join other international efforts currently pursuing this goal using a novel approach, which combines the sensitivity of bolometric detectors with the control of systematic effects provided by interferometry. After its current calibration phase is completed a technological demonstrator already constructed in European laboratories will be deployed in Alto Chorrillos, a site in the Puna near San Antonio de los Cobres, Salta, Argentina. The complete first module of the instrument is planned to be installed during 2020. We review the scientific goals of the project, the instrument design and its expected performance.

Inflationary equilibrium configurations of scalar-tensor theories of gravity

In this paper we investigate the asymptotic dynamics of inflationary cosmological models that are based in scalar-tensor theories of gravity. Our main aim is to explore the global structure of the phase space in the framework of single-field inflation models. For this purpose we make emphasis in the adequate choice of the variables of the phase space. Our results indicate that, although single-field inflation is generic in the sense that the corresponding critical point in the phase space exists for a wide class of potentials, along given phase space orbits -- representing potential cosmic histories -- the occurrence of the inflationary stage is rather dependent on the initial conditions. We have been able to give quantitative estimates of the relative probability (RP) for initial conditions leading to slow-roll inflation. For the non-minimal coupling model with the $\phi^2$-potential our rough estimates yield to an almost vanishing relative probability: $10^{-13}\,\%\lesssim RP\ll 10^{-8}\,\%$. These bonds are greatly improved in the scalar-tensor models, including the Brans-Dicke theory, where the relative probability $1\,\%\lesssim RP\leq 100\,\%$. Hence slow-roll inflation is indeed a natural stage of the cosmic expansion in Brans-Dicke models of inflation. It is confirmed as well that the dynamics of vacuum Brans-Dicke theories with arbitrary potentials are non-chaotic.

The exact solutions in verified cosmological models based on generalized scalar-tensor gravity

We consider the cosmological models built on the basis of scalar-tensor gravity, in which the non-minimal coupling of a scalar field and the Ricci scalar leads to the evolution of the field, the deviation of its potential from the flat shape and the difference in the dynamics of the early universe from pure exponential expansion. It is shown that such models are in a good agreement with modern observational data. As an example of the application of the proposed approach, the exact solutions for the different models of cosmological inflation were obtained.

Galileon scalar electrodynamics

We construct a consistent model of Galileon scalar electrodynamics. The model satisfies three essential requirements: (1) The action contains higher-order derivative terms, and obey the Galilean symmetry, (2) Equations of motion also satisfy Galilean symmetry and contain only up to second-order derivative terms in the matter fields and, hence do not suffer from instability, and (3) local U(1) gauge invariance is preserved. We show that the non-minimal coupling terms in our model are different from that of the real scalar Galileon models; however, they match with the Galileon real scalar field action. We show that the model can lead to an accelerated expansion in the early Universe. We discuss the implications of the model for cosmological inflation.

Irreversible thermodynamical description of warm inflationary cosmological models

We investigate the interaction between scalar fields and radiation in the framework of warm inflationary models by using the irreversible thermodynamics of open systems with matter creation/annihilation. We consider the scalar fields and radiation as an interacting two component cosmological fluid in a homogeneous, spatially flat and isotropic Friedmann-Robertson-Walker (FRW) Universe. The thermodynamics of open systems as applied together with the gravitational field equations to the two component cosmological fluid leads to a generalization of the elementary scalar field-radiation interaction model, which is the theoretical basis of warm inflationary models, with the decay (creation) pressures explicitly considered as parts of the cosmological fluid energy-momentum tensor. Specific models describing coherently oscillating scalar waves, scalar fields with a constant potential, and scalar fields with a Higgs type potential are considered in detail. For each case exact and numerical solutions of the gravitational field equations with scalar field-radiation interaction are obtained, and they show the transition from an accelerating inflationary phase to a decelerating one. The theoretical predictions of the warm inflationary scenario with irreversible matter creation are also compared in detail with the Planck 2018 observational data, and constraints on the free parameters of the model are obtained.

Gravitational Wave from Cosmic Inflation in a Gravity with Two Small Four-derivative Corrections

We investigate a model of inflationary cosmology where the minimally coupled scalar field theory is modified by additional correction terms. Among the most general ten correction terms remarked by Weinberg in context of effective field theory, we consider only two terms, $f_1(\phi) R^2$ and $f_2(\phi) R^{ab}R_{ab}$, following the work by Noh and Hwang where $f_1$ and $f_2$ are constant. The fourth order differential equations for the background universe and the tensor-type perturbation are derived out of this model. We show that these equations can be reduced to second order equations, supposing that $f_n$ are small. From these approximated equations, we find that the propagation speed of gravitational wave is slightly less than the speed of light due to $f_2$ term, and that the evolution of the tensor-type perturbation is conserved in the large scale limit.

Temporally varying universal gravitational “constant” and speed of light in energy momentum squared gravity

Energy Momentum Squared Gravity (EMSG) is a cosmological model where the scale factor is non vanishing at all times and hence does not favor big bang cosmology. However, the profile of density in the radiation dominated universe shows that EMSG supports inflationary cosmology. Inflationary cosmological models are successful in providing convincing answers to major cosmological issues like horizon problem, flatness problem and small value of cosmological constant but hitherto no model of inflation has been observationally confirmed. Owing to this, Varying Speed of Light (VSL) were introduced which are a class of cosmological models which disfavor inflation and propose an alternative route to solve these cosmological issues by just allowing the speed of light (and Newtonian Gravitational constant) to vary. VSL theories were motivated to address the shortcomings of inflation but do not address the shortcomings related to the initial big bang singularity. In this spirit, we present here a novel cosmological model which is free from both the "initial big bang singularity" and "inflation" by incorporating a mutually varying speed of light $c(t)$ and Newtonian gravitational constant $G(t)$ in the framework of EMSG. We report that in EMSG, for a dust universe ($\omega=0$), cosmological models for a time varying $c(t)$ and $G(t)$ and constant $c$ and $G$ are indistinguishable, whereas for a radiation dominated universe ($\omega = 1/3$), a mutually varying $c(t)$ and $G(t)$ provides an exiting alternative to inflationary cosmology which is also free from initial big bang singularity. We further report that for an ansatz of scale factor representing a bouncing cosmological model, the VSL theory can be applied to a quadratic $T$ gravity model to get rid of "inflation" and "big bang singularity" and concurrently solve the above mentioned cosmological enigmas.

Exploring suppressed long-distance correlations as the cause of suppressed large-angle correlations

ABSTRACT The absence of large-angle correlations in the map of cosmic microwave background temperature fluctuations is among the well-established anomalies identified in full-sky and cut-sky maps over the past three decades. Suppressed large-angle correlations are rare statistical flukes in standard inflationary cosmological models. One natural explanation could be that the underlying primordial density perturbations lack correlations on large distance scales. To test this idea, we replace Fourier modes by a wavelet basis with compact spatial support. While the angular correlation function of perturbations can readily be suppressed, the observed monopole- and dipole-subtracted correlation function is not generally suppressed. This suggests that suppression of large-angle temperature correlations requires a mechanism that has both real-space and harmonic-space effects.

Generalized dilaton\u2013axion models of inflation, de Sitter vacua and spontaneous SUSY breaking in supergravity

We propose the unified models of cosmological inflation, spontaneous SUSY breaking, and the dark energy (de Sitter vacuum) in N=1 supergravity with the dilaton–axion chiral superfield T in the presence of an N=1 vector multiplet with the alternative Fayet–Iliopoulos term. By using the Kähler potential as K=-alpha log (T+overline{T}) and the superpotential as a sum of a constant and a linear term, we find that viable inflation is possible for 3le alpha le alpha _mathrm{max} where alpha _mathrm{max}approx 7.235. Observations of the amplitude of primordial scalar perturbations fix the SUSY breaking scale in our models as high as 10^{13} hbox {GeV}. In the case of alpha >3 the axion gets the tree-level (non-tachyonic) mass comparable to the inflaton mass.