Imprints of cosmic phase transition in inflationary gravitational waves

We discuss the effects of cosmic phase transition on the spectrum of primordial gravitational waves generated during inflation. The energy density of the scalar condensation responsible for the phase transition may become sizable at the epoch of phase transition, which significantly affects the evolution of the universe. As a result, the amplitudes of the gravitational waves at high frequency modes are suppressed. Thus the gravitational wave spectrum can be a probe of phase transition in the early universe.     

The CST bounce universe model——A parametric study

A bounce universe model with a scale-invariant and stable spectrum of primordial density perturbations was constructed using a consistent truncation of the D-brane dynamics from Type IIB string theory. A coupling was introduced between the tachyon field and the adjoint Higgs field on the D3-branes to lock the tachyon at the top of its potential hill and to model the bounce process,which is known as the Coupled Scalar and Tachyon Bounce(CSTB) Universe. The CSTB model has been shown to be ghost free,and it fulfils the null energy condition; in addition, it can also solve the Big Bang cosmic singularity problem. In this paper we conduct an extensive follow-up study of the parameter space of the CSTB model. In particular we are interested in the parameter values that can produce a single bounce to arrive at a radiation-dominated universe. We further establish that the CSTB universe is a viable alternative to inflation, as it can naturally produce a sufficient number of e-foldings in the locked inflation epoch and in the post-bounce expansion to overcome the four fundamental limitations of the Big Bang cosmology, which are flatness, horizon,homogeneity and singularity, resulting in a universe of the current size.     

Gravitational energy in the expanding universe

The role of gravitational energy in the evolution of the universe is examined. In co-moving coordinates, calculation of the Landau-Lifshitz pseudotensor for FRW models reveals that: (i) the total energy of a spatially closed universe irrespective of the equation of state of the cosmic fluid is zero at all times, (ii) the total energy enclosed within any finite volume of the spatially flat universe is zero at all times, (iii) during inflation the vacuum energy driving the accelerated expansion and ultimately responsible for the creation of matter (radiation) in the universe, is drawn from the energy of the gravitational field. In a similar fashion, certain cosmological models which abandon adiabaticity by allowing for particle creation, use the gravitational energy directly as an energy source.     

Inflation,quantum fields,and CMB anisotropies

Inflationary cosmology has proved to be the most successful at predicting the properties of the anisotropies observed in the cosmic microwave background (CMB). In this essay we show that quantum field renormalization significantly influences the generation of primordial perturbations and hence the expected measurable imprint of cosmological inflation on the CMB. However, the new predictions remain in agreement with observation, and in fact favor the simplest forms of inflation. In the near future, observations of the influence of gravitational waves from the early universe on the CMB will test our new predictions.     

Eternal inflation and the quantum birth of cosmic structure

We consider the eternal inflation scenario of the slow-roll/chaotic type with the additional element of an objective collapse of the wave function. The incorporation of this new agent to the traditional inflationary setting might represent a possible solution to the quantum measurement problem during inflation, a subject that has not reached a consensus among the community. Specifically, it could provide an explanation for the generation of the primordial anisotropies and inhomogeneities, starting from a perfectly symmetric background and invoking symmetric dynamics. We adopt the continuous spontaneous localization model, in the context of inflation, as the dynamical reduction mechanism that generates the primordial inhomogeneities. Furthermore, when enforcing the objective reduction mechanism, the condition for eternal inflation can be bypassed. In particular, the collapse mechanism incites the wave function, corresponding to the inflaton, to localize itself around the zero mode of the field. Then the zero mode will evolve essentially unperturbed, driving inflation to an end in any region of the Universe where inflation occurred. Also, our approach achieves a primordial spectrum with an amplitude and shape consistent with the one that best fits the observational data.     

Why concave rather than convex inflaton potential?

The Planck data on cosmic microwave background indicates that the Starobinsky-type model with concave inflation potential is favored over the convex-type chaotic inflation. Is there any reason for that? Here we argue that if our universe began with a Euclidean wormhole, then the Starobinsky-type inflation is probabilistically favored. It is known that for a more generic choice of parameters than that originally assumed by Hartle and Hawking, the Hartle–Hawking wave function is dominated by Euclidean wormholes, which can be interpreted as the creation of two classical universes from nothing. We show that only one end of the wormhole can be classicalized for a convex potential, while both ends can be classicalized for a concave potential. The latter is therefore more probable.     

On primordial black holes and secondary gravitational waves generated from inflation with solo/multi-bumpy potential

It is well known that a primordial black hole (PBH) can be generated in the inflation process of the early universe, especially when the inflation field has a number of non-trivial features that could break the slow-roll condition. In this study, we investigate a toy model of inflation with bumpy potential, which has one or several bumps. We determined that the potential with multi-bump can generate power spectra with multi-peaks in small-scale region, which can in turn predict the generation of primordial black holes in various mass ranges. We also consider the two possibilities of PBH formation by spherical and elliptical collapses. Finally, we discuss the scalar-induced gravitational waves (SIGWs) generated by linear scalar perturbations at second-order.     

Position-space description of the cosmic microwave background and its temperature correlation function

We suggest that the cosmic microwave background (CMB) temperature correlation function C(theta) as a function of angle provides a direct connection between experimental data and the fundamental cosmological quantities. The evolution of inhomogeneities in the prerecombination universe is studied using Green's functions in position space. We find that a primordial adiabatic point perturbation propagates as a sharp-edged spherical acoustic wave. Density singularities at its wave fronts create a feature in the CMB correlation function distinguished by a dip at theta approximately 1.2 degrees. Characteristics of the feature are sensitive to the values of cosmological parameters, in particular to the total and the baryon densities.     

Gauge fields and inflation

The isotropy and homogeneity of the cosmic microwave background (CMB) favors “scalar driven” early Universe inflationary models. However, gauge fields and other non-scalar fields are far more common at all energy scales, in particular at high energies seemingly relevant to inflation models. Hence, in this review we consider the role and consequences, theoretical and observational, that gauge fields can have during the inflationary era. Gauge fields may be turned on in the background during inflation, or may become relevant at the level of cosmic perturbations. There have been two main classes of models with gauge fields in the background, models which show violation of the cosmic no-hair theorem and those which lead to isotropic FLRW cosmology, respecting the cosmic no-hair theorem. Models in which gauge fields are only turned on at the cosmic perturbation level, may source primordial magnetic fields. We also review specific observational features of these models on the CMB and/or the primordial cosmic magnetic fields. Our discussions will be mainly focused on the inflation period, with only a brief discussion on the post inflationary (p)reheating era.     

宇宙创生于真空涨落的一个可能方案——原初暴涨宇宙模型

大爆炸宇宙模型的成功说明宇宙有可能是创生出来的。宇宙究竟是创生于“无”,还是创生于真空涨落?这是目前正在热烈讨论的问题。本文提出宇宙创生于真空涨落的一种可能的方案。我们提出,在单圈近似下的真空涨落创生了原初暴涨宇宙—原初deSitter宇宙,这时SO₁₁,SU₁₄或E₈×E₈对称性成立。由于规范耦合常数g和Higgs场自耦合常数λ的渐近自由,将使得原初大统一破缺发生一级相变,相变时释放出的潜热化为宇宙的原初物质,以使宇宙升温到接近Planck温度。这样所创生的宇宙即由原初暴涨阶段过渡到以辐射为主的标准模型。此后,例如SU₅GUT成立,在创生后的10^-35秒,将发生熟知的第二次暴涨。 关键词：     

Quantum Creation of Closed Universe with Both Effects of Tunnelling and Well

A new “twice loose shoe“ method in the Wheeler-DeWitt equation of the universe wavefunction on the cosmic scale factor a and a scalar field φ is suggested,We analyze both the affections coming from the tunnelling effect of α and the potential well effect of φ,and obtain the initial values α0 about a primary closed universe which is born with the largest probability in the quantum manner,Our result is able to overcome the “large field difficulty“ of the universe quantum creation probabiltiy with only tunnelling effect.This new born universe has to suffer a startup of inflation,and then comes into the usual slow rolling inflation.The universe with the largest probalility maybe has a “gentle“ inflation of an eternal chaotic infltion.this depends on a new parameter q which describes the tunnelling character.     

Primordial shear and the question of inflation

The role of primordial shear in two inflationary scenarios, Planck-time (Linde) inflation and the GUT inflation is discussed. In the Linde picture, including a simple “particle creation” term produces universes in which the temperature rapidly attains a stable asymptotic value just below the Planck temperature, whatever the Higgs field coupling constant. Such universes are truly isotropic by the time the GUT era is reached. (There is no supercooling because of particle creation.) In the GUT picture, inflation can occur notwithstanding the presence of anisotropy. However, in these models, initial anisotropy reduces the GUT era coherence length and it becomes more difficult to form the present universe from a single bubble.     

Implications of cosmic string-induced density fluctuations at the quark-hadron transition

We show that cosmic strings moving through the plasma at the time of a first-order quark-hadron transition in the early universe generate baryon inhomogeneities, which can survive till the nucleosynthesis epoch. We find out how these inhomogeneities actually affect the calculated values of the light element abundances. Recently a wealth of observational data from various experiments have helped to reduce the uncertainties in the values of these abundances. Using these we show that it is possible to derive constraints in the presence of cosmic strings during the quark-hadron transition.     

Remarks on the Idea of Spontaneous Break-Down of Symmetry,Cosmic Variability of Eddington's Number,Mach's Idea Concering the Origin of Inertia,and Field Equations Describing Global and Local Gravitational Fields

Subject is considered on the level of classical field theory. We start from some aspects of the theory of ferromagnets. Their counterpart in classical field theory is pointed out using the over simplified model of a selfinteracting scalar field. The ground state (“vacuum expection value”) of the scalar field is interpreted as cosmic background field, which can be considered as constant for local physical phenomena. In practice, however, it is a function of the age of universe. Which kind of function it could be is suggested by a discussion of the cosmic variability of Eddington's number γ = 10⁴⁰, which refers to Dirac's consideration of this problem. But contrary to Dirac's assumption that atomic quantities are constant, we suppose that the inertial mass of elementary particles is a function of the age of universe. The cosmic gravitational field is described by other equations than the gravitational field created by local matter distributions. The field equations for the local gravitational field we start from reduce to Einstein's equations, if we neglect the possible influence of the universe on local phenomena. In case that the cosmic matter is homogeneously and isotropically distributed, the field equations for the cosmic gravitational field permit only such a time dependent solution the three-spaces of which are linearly expanding and spherically closed. The different field equations for cosmic and local gravitational fields are considered approximations of more fundamental field equations which approximately split into two sets of equations, if it is possible to contrast local physical systems with the universe. The described cosmological model taken as a basis, the inertial mass of elementary particles becomes a function of the matter density creating the cosmic gravitational field. This could be considered as, at least, partly realisation of Mach's idea concerning the origin of inertia. Starting from the interpretation of the ground state (vacuum expection value) as a function of a certain cosmic background field, more realistic gage field models could give the following picture of cosmic development: In the far past there was a state of the universe characterized by enormous contraction of matter. In this stage of development, it was impossible to contrast particles with the universe. Matter expands and it becomes possible to contrast certain physical systems with the universe. But the ground state is such a symmetric one that only fields with vanishing rest mass can be contrasted with the universe (ferromagnet above Curie temperature). With further expansion of the universe the ground state will lose certain symmetry properties. By this it becomes possible that you get the impression there are particles with nonvanishing rest mass (ferromagnet below Curie temperature). Finally, the influence of the universe on local physical systems goes to zero with further expansion. Especially, this means the inertial mass of elementary particles goes to zero, too (Curie temperature of ferromagnetic material goes to zero with cosmic expansion).     

A universe embedded in a five-dimensional flat space

Since a homogeneous isotropic universe can be embedded in a flat space of five dimensions, the question is considered under what conditions a more general universe can be embedded in a five-dimensional flat space. On the assumption that the deviation from homogeneity is small, it is found that real inhomogeneities can occur only in the case of a universe filled with radiation, or a universe containing at least two different substances with different equations of state, as for example radiation and matter. In the case of a radiation-filled universe, the inhomogeneities can be of arbitrary size and can conceivably be the precursors of galaxies.     

Exploring bouncing cosmologies with cosmological surveys

From recent observational data two significant directions have been made in the field of theoretical cosmology recently.First,we are now able to make use of present observations,such as the Planck and BICEP2 data,to examine theoretical predictions from the standard inflationaryΛCDM which were made decades of years ago.Second,we can search for new cosmological signatures as a way to explore physics beyond the standard cosmic paradigm.In particular,a subset of early universe models admit a nonsingular bouncing solution that attempts to address the issue of the big bang singularity.These models have achieved a series of considerable developments in recent years,in particular in their perturbative frameworks,which made brand-new predictions of cosmological signatures that could be visible in current and forthcoming observations.Herein we present two representative paradigms of early universe physics.The first is the reputed new matter(or matter-ekpyrotic)bounce scenario in which the universe starts with a matter-dominated contraction phase and transitions into an ekpyrotic phase.In the setting of this paradigm,we have proposed some possible mechanisms of generating a red tilt for primordial curvature perturbations and confront the general predictions with recent cosmological observations.The second is the matter-bounce inflation scenario which can be viewed as an extension of inflationary cosmology with a matter contraction before inflation.We present a class of possible model constructions and review the implications on the current CMB experiments.Lastly a review of significant achievements of these paradigms beyond the inflationaryΛCDM model is made,which is expected to shed new light on the future direction of observational cosmology.     

Particle Creation in the Oscillatory Phase of Inflaton

A thermal squeezed state representation of inflaton is constructed for a flat Friedmann–Robertson–Walker (FRW) background metric and the phenomenon of particle creation is examined during the oscillatory phase of inflaton, in the semiclassical theory of gravity. An approximate solution to the semiclassical Einstein equation is obtained in thermal squeezed state formalism perturbatively and is found obey the same power-law expansion as that of classical Einstein equation. In addition to that the solution shows oscillatory in nature except on a particular condition. It is also noted that, the coherently oscillating nonclassical inflaton, in thermal squeezed vacuum state, thermal squeezed state, and thermal coherent state, suffers particle production and the created particles exhibit oscillatory behavior. The present study can account for the postinflation particle creation due to thermal and quantum effects of inflation in a flat FRW universe.     

Scalar and spinor fields in the very early universe

Here it is shown how the vacuum energy may dominate the energy density of the very early universe even when the Higg's field in the Coleman-Weinberg potential is confined near the origin at extremely high temperature and the inflationary scenario may start. Also it is shown that supersymmetry breaking may be responsible for this phenomenon. Thus it provides another support for the hypothesis of primordial inflation proposed by Ellis et al. [4],