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.     

第四讲暴涨宇宙学的研究与进展

文章简单介绍了标准(大爆炸)宇宙模型的成功和困难，着重介绍了暴涨宇宙学的研究历史和最近的进展，并展望了今后人们可能的关注方向     

Scalar field fluctuations in the expanding universe and the new inflationary universe scenario

The behaviour of the scalar fied fluctuations in the exponentially expanding universe and their role in the new inflationary universe scenario are investigated.     

The warm inflationary universe

In the past decade, the importance of dissipation and fluctuation to inflationary dynamics has been realized and has led to a new picture of inflation called warm inflation. Although these phenomena are common to condensed matter systems, for inflation models their importance has only recently started to be appreciated. The article describes the motivation for these phenomena during inflation and then examines their origins from first principles quantum field theory treatments of inflation models. Cosmology today is a data intensive field and this is driving theory to greater precision and predictability. This opens the possibility to consider tests for detecting observational signatures of dissipative processes, which will be discussed. In addition, it will be discussed how particle physics and cosmology are now working in tandem to push the boundaries of our knowledge about fundamental physics.     

Tachyon-Chaplygin inflationary universe model

Tachyonic inflationary universe model in the context of a Chaplygin gas equation of state is studied. General conditions for this model to be realizable are discussed. By using an effective exponential potential we describe in great details the characteristic of the inflationary universe model. The parameters of the model are restricted by using recent astronomical observations.     

Fluctuations in the inflationary universe

In the usual treatment of the inflationary universe, it is assumed that the expectation value of some component of the Higgs field develops a non-zero symmetry breaking value Φ₀. However, in the models normally considered, the expectation value of Φ will be zero at all times because Φ and ?Φ are equally probable. To overcome this difficulty, we calculate the effective action as a function of 〈Φ²〉 rather than 〈Φ〉. This also solves the infra-red problem associated with a Coleman-Weinberg condition in de Sitter space. The expectation value of Φ² grows linearly with time at first and then as (t₂ ? t^?1). The irregularities in the resulting universe are smaller than those predicted by previous authors, though in the case of the standard SU(5) GUT they are still bigger than the limit set by the microwave background.     

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.     

Cosmological perturbations in the inflationary universe

In the framework of the gauge-invariant formalism the problem of the evolution of adiabatic perturbations in the metric for the theory of gravity with higher derivatives, which contains inflation, has been solved. The results are compared with the case when inflation arises due to a scalar field. The restrictions on the parameters of the models are given.     

Baryon asymmetry in the inflationary universe

It is shown that the baryon asymmetry in the inflationary universe under certain constraints on the masses of superheavy bosons can be larger than that in the standard baryosynthesis scenario. An important property of the model considered is that the final baryon asymmetry does not depend on initial conditions in the early universe in contrast to what occurs in the standard scenario based on B?L conserving GUTs.     

Fluctuations in a supersymmetric inflationary universe

It has been demonstrated that fluctuations in the new inflationary universe may be almost scale-invariant, but are unfortunately too large. We show that supersymmetric inflationary models allow the fluctuations to be smaller. In a toy supersymmetric model, the perturbations are O(10⁻⁴) is the Yukawa interactions are O(10⁻⁶μ/m_p) where μ is the magnitude of the Higgs vacuum expectation value driving the inflation. It is therefore easier to have small fluctuations if inflation occurs close to the Planck epoch.     

Quantum fluctuations in the new inflationary universe

The evolution of quantum fluctuations of a scalar field in de Sitter space is analyzed in the context of the new inflationary scenario. The duration of the inflationary phase is estimated and the problem of density perturbations resulting from quantum fluctuations of the Higgs field is discussed.     

Interacting tachyonic scalar field

We discuss the coupling between dark energy and matter by considering a homogeneous tachyonic scalar field as a candidate for dark energy.We obtained the functional form of scale factor by assuming that the coupling strength depends linearly on the Hubble parameter and energy density.We also estimated the cosmic age of the Universe for different values of coupling constant.     

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.     

Limits on inflationary models of the universe

It is shown that there are severe limits on any model in which the universe undergoes a period of exponential expansion in the early stages. If one requires that the exponential expansion is long enough to account for the spatial flatness of the universe and that it should not create larger density fluctuations than are observed, it follows that the Hubble constant during the exponential expansion cannot be greater than 6 × 10^?5 of the Planck mass. This rules out all models in which the Hubble constant is of the order of the Planck mass. It is shown that one can satisfy the limits with a model containing a massive scalar field if the mass of the field is less than about 10¹⁴ GeV.     

The fractal dimension of the inflationary universe

In cosmological scenarios of the new inflationary type, inflation never ends completely. The total volume of inflating regions grows exponentially with time, and they form a self-similar fractal of dimension slightly less than 3.     

Warm-intermediate inflationary universe model with viscous pressure in high dissipative regime

Warm inflation model with bulk viscous pressure in the context of “intermediate inflation” where the cosmological scale factor expands as $a(t)=a_0\exp (At^f)$ , is studied. The characteristics of this model in slow-roll approximation and in high dissipative regime are presented in two cases: 1—Dissipative parameter $\Gamma $ as a function of scalar field $\phi $ and bulk viscous coefficient $\zeta $ as a function of energy density $\rho $ . 2— $\Gamma $ and $\zeta $ are constant parameters. Scalar, tensor perturbations and spectral indices for this scenario are obtained. The cosmological parameters appearing in the present model are constrained by recent observational data (WMAP7).     

Coleman-Weinberg theory and the new inflationary universe scenario

It is argued that a new inflationary universe scenario, which provides a possible solution of the horizon, flatness, homogeneity, isotropy and primordial monopole problems, can be naturally implemented in the context of grand unified theories of the type of the Coleman-Weinberg theory.