Closed inflationary universe in patch cosmology

In this paper, we study closed inflationary universe models using the Gauss–Bonnet Brane. We determine and characterize the existence of a universe with Ω>1, with an appropriate period of inflation. We have found that this model is less restrictive in comparison with the standard approach where a scalar field is considered. We use recent astronomical observations to constrain the parameters appearing in the model.     

Axially Symmetric Inflationary Universe in General Relativity

We have investigated a simple axially symmetric inflationary universe in the presence of mass less scalar field with a flat potential. To get an inflationary universe, we have considered a flat region in which potential V is constant. Some physical properties of the universe are also discussed.     

The evolution of the universe from non-compact Kaluza-Klein theory

We develop a 5D mechanism, inspired by Campbells theorem, to explain the (neutral scalar field governed) evolution of the universe from an initially inflationary expansion that has a change of phase towards a decelerated expansion and thereafter evolves towards the present day observed accelerated (quintessential) expansion.Received: 4 October 2004, Published online: 23 November 2004PACS: 04.20.Jb, 11.10.Kk, 98.80.Cq     

Constructing Phantom With a Nonminimally Coupled Complex Scalar Field

In view of the recent observation data indicating that the equation of state of the dark energy might be smaller than −1, this leads to introduction of phantom models featured by their negative kinetic energy to account for the regime of equation of state w < −1. In this paper, we discuss the possibility of using a nonminimally coupled complex scalar field as phantom to realize the equation-of-state parameter w < −1. The main equations which govern the evolution of the universe are obtained. The relations between the potential of the field and red-shift, namely, the reconstruction equations are derived. PACS 04.40.-b, 98.80.Cq, 98.80.Hw     

Induced inflation from a 5D purely kinetic scalar field formalism on warped product spaces

Considering a separable and purely kinetic 5D scalar field we investigate the induction of 4D scalar potentials on a 4D constant foliation on the class of 5D warped product space-times. We obtain a quantum confinement of the inflaton modes given naturally from the model for at least a class of warping factors. We can recover a 4D inflationary scenario where the inflationary potential is geometrically induced from 5D and the effective equation of state in 4D that includes the effect of the inflaton field and the induced matter is P_eff≃-ρ_eff. PACS 04.20.Jb; 11.10.kk; 98.80.Cq     

A Higher Dimensional Inflationary Universe in General Relativity

A five dimensional Kaluza-Klein inflationary universe is investigated in the presence of massless scalar field with a flat potential. To get an inflationary universe a flat region in which potential V is constant is considered. Some physical and kinematical properties of the universe are also discussed.     

Warm-intermediate inflationary universe model in braneworld cosmologies

Warm-intermediate inflationary universe models in the context of braneworld cosmologies are studied. This study is done in the weak and strong dissipative regimes. We find that the scalar potentials and dissipation coefficients in terms of the scalar field evolve as type-power-law and powers of logarithms, respectively. General conditions required for these models to be realizable are derived and discussed. We also study the scalar and tensor perturbations for each regime. We use recent astronomical observations to constrain the parameters appearing in the braneworld models.     

Can Inflation, Dark Matter and Dark Energy Be Described in Terms of a Single, Real Scalar Field?

In this article, our aim is to consider inflation, dark energy and dark matter in the framework of a real scalar field. To this end, we use the quintessence approach. We have tried a real scalar field with a specific self-interaction potential in a spacially flat universe. Numerical results indicate that this potential can drive the expansion of the universe in three distinct phases. The first phase behaves as an inflationary expansion. For this stage, setting the scalar field’s initial value to ϕ ₀≥1.94 leads to N 3 68\mathcal{N}\geq 68 favored by observation. After the inflationary phase, the scalar field starts an oscillatory behavior which averages to a =0\bar{w}=0 fluid. This stage can be taken as a cold dark matter (p≈0) epoch expected from works on the structure formation issue. Observations and cosmological models indicate that t _inf ≈10⁻³⁵ s and the matter dominated lasts for t _m ≈10¹⁷ s, hence (\fract_mt_inf)_obs ? 10⁵²(\frac{t_{m}}{t_{inf}})_{obs}\approx10^{52}. We have shown that the present model can satisfy such a constraint. Finally, the scalar field leaves the oscillatory behavior and once again enters a second inflationary stage which can be identified with the recent accelerated expansion of the universe. We have also compared our model with the ΛCDM model and have found a very good agreement between the equation of state parameter of both of models during the DM and DE era.     

On quintessential cosmological models and exponential potentials

We first study dark energy models with a minimally-coupled scalar field and generalized exponential potentials, admitting exact solutions for the cosmological equations: actually, it turns out that for this class of potentials the Einstein field equations exhibit alternative Lagrangians, and are completely integrable and separable. We analyze their analytical solutions, especially discussing when they are compatible with a late time quintessential expansion of the universe. As a further issue, we discuss how quintessential scalar fields with exponential potentials can be connected to the inflationary phase, building up a quintessential inflationary scenario: actually, it turns out that the transition from inflation toward late-time exponential quintessential tail admits a kination period, which is an indispensable ingredient of this kind of theoretical models. All such considerations have been made by including also radiation into the model.     

Wave Functions for Arbitrary Operator Ordering in the de Sitter Minisuperspace Approximation

We derive exact series solutions for the Wheeler–DeWitt equation corresponding to a spatially closed Friedmann–Robertson–Walker universe with cosmological constant for arbitrary operator ordering of the scale factor of the universe. The resulting wave functions are those relevant to the approximation which has been widely used in two-dimensional minisuperspace models with an inflationary scalar field for the purpose of predicting the period of inflation which results from competing boundary condition proposals for the wave function of the universe. The problem that Vilenkin's tunneling wave function is not normalizable for general operator orderings, is shown to persist for other values of the spatial curvature, and when additional matter degrees of freedom such as radiation are included.     

The evolution equation of the scalar field in the new inflationary universe

We derive an effective evolution equation for the scalar field driving inflation in the new inflationary universe. We use a perturbative calculation scheme proposed recently by Morikawa and Sasaki. The relevant initial conditions and dynamical constraints for the Coleman-Weinberg effective potential to appear in the evolution equation are discussed as well as the form of the particle production damping term. The validity of these conditions in the new inflationary universe model is discussed.     

Dynamical mechanism for varying light velocity as a solution to cosmological problems

A dynamical model for varying light velocity in cosmology is developed, based on the idea that there are two metrics in spacetime. One metric g_μν describes the standard gravitational vacuum, and the other describes the geometry through which matter fields propagate. Matter propagating causally with respect to can provide acausal contributions to the matter stress-energy tensor in the field equations for g_μν, which, as we explicitly demonstrate with perfect fluid and scalar field matter models, provides a mechanism for the solution of the horizon, flatness and magnetic monopole problems in an FRW universe. The field equations also provide a ‘graceful exit' to the inflationary epoch since below an energy scale (related to the mass of ψ_μ) we recover exactly the standard FRW field equations.     

Dark Energy Model with Canonical Scalar Field and Non-Linear Born–Infeld Type Scalar Field

In this paper, we propose the non-linear Born–Infeld scalar field and canonical scalar field dark energy models with the potential , which admits late time de Sitter attractor solution. The attractor solution corresponds to an equation of state ω_φ → − 1 and a cosmic density parameter Ω_φ → 1, which are important features for a dark energy model that can meet the current observations. dark energy; canonical scalar field, non-linear Born–Infeld type scalar field, attractor solution. PACS number(s):98.80.-k; 98.80.Cq; 98.80.Es.     

Bianchi type I inflationary universe in general relativity

In this paper, we have investigated Bianchi type I inflationary universe in the presence of massless scalar field with a flat potential. To get an inflationary solution, we have considered a flat region in which potential V is constant. The inflationary scenario of the model is discussed in detail.     

Anisotropic Inflationary Scenario Via Generalized Chaplygin Gas Model

We investigate generalized chaplygin gas for warm inflationary scenario in the context of locally rotationally symmetric Bianchi type I universe model.We assume two different cases of dissipative coefficient,i.e.,constant as well as function of scalar field.We construct dynamical equations as well as a relationship between scalar and radiation energy densities under slow-roll approximation.We also derive slow-roll parameters,scalar and tensor power spectra,scalar spectral index,tensor to scalar ratio for analyzing inflationary background during high dissipative regime.We also use the WMAP7 data for the discussion of our parameters.     

Iso-Spectral Potentials and Inflationary Quantum Cosmology

Using the factorization approach of quantum mechanics, we obtain a family of isospectral scalar potentials for power law inflationary cosmology. The construction is based on a scattering Wheeler-DeWitt solution. These iso-potentials have new features, they give a mechanism to end inflation, as well as the possibility to have new inflationary epochs. The procedure can be extended to other cosmological models. PACS numbers: 02.30.Jr; 04.60.Ds; 04.60.Kz; 98.80.Cq.     

Quantum gravitational contributions to the cosmic microwave background anisotropy spectrum

We derive the primordial power spectrum of density fluctuations in the framework of quantum cosmology. For this purpose we perform a Born-Oppenheimer approximation to the Wheeler-DeWitt equation for an inflationary universe with a scalar field. In this way, we first recover the scale-invariant power spectrum that is found as an approximation in the simplest inflationary models. We then obtain quantum gravitational corrections to this spectrum and discuss whether they lead to measurable signatures in the cosmic microwave background anisotropy spectrum. The nonobservation so far of such corrections translates into an upper bound on the energy scale of inflation.     

Einstein gravity as spontaneously broken Weyl gravity

We study the locally conformal invariant Weyl theory of gravitation and introduce a conformally coupled scalar field. Einstein gravity is induced by spontaneous breaking of the local conformal symmetry in an effective long range approximation. The effective potential for the scalar field is calculated at the one-loop level up to curvature squared in order in an arbitrary curved background. The non-zero vacuum expectation value of the scalar field induces the dimensional Einstein's gravitational coupling constant stably in case ofR > 0. ForR < 0, the phase transition occurs from the symmetric phase to the broken phase as the curvature decreases. This theory may be an attractive candidate for the primordial inflationary universe scenario.