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.     

Generation of isothermal density perturbations in the inflationary universe

It is shown that not only adiabatic perturbations of the density but also isothermal density perturbations are generated in the inflationary universe. The magnitude of isothermal perturbations can be sufficiently large for the subsequent galaxy formation. The spectrum of isothermal perturbations can differ considerably from a flat one.     

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.     

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     

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.     

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.     

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.     

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.     

Fate of order parameter in the inflationary universe

We evaluate the friction term of the evolution equation of the order parameter in the new inflationary universe scenario. It is shown that the friction force is too weak so that the order parameter travels many time around minima of the Coleman-Weinberg potential. It causes unwanted large scale inhomogeneities. Reheating of the universe is also discussed.     

Nonflat perturbations in inflationary cosmology

The generation of initial perturbations in inflationary cosmological models in the presence of fluctuations of several scalar fields is considered. It is shown that there is a possibility to build the model-dependent spectrum both of adiabatic (inflation) and isothermal (isoinflaton) density perturbations, containing a separate maximum, large-scale power or increasing at large (at small) wavelengths, which are of essential interest for the theory of the large-scale structure of the Universe.     

Measuring the geometry of the universe in the presence of isocurvature modes

The cosmic microwave background (CMB) anisotropy constrains the geometry of the Universe because the positions of the acoustic peaks of the angular power spectrum depend strongly on the curvature of three-dimensional space. In this Letter we exploit current observations to determine the geometry in the presence of isocurvature modes. Most previous analyses assumed that the primordial perturbations were adiabatic. A priori one might expect that allowing isocurvature modes would substantially degrade constraints on the curvature. We find, however, that with additional data sets, the geometry remains well constrained. When the most general isocurvature perturbation is allowed, the CMB alone can only poorly constrain the geometry to . Including large-scale structure data, one obtains Ohm(0) = 1.07 +/- 0.03, and 1.06 +/- 0.02 when supplemented by supernova data and the determination of H(0).     

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.     

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.     

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 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.