QUANTUM COSMOLOGY WITH O_(8N+1)- SYMMETRIC COUPLING SCALAR FIELD

Using the Hartle-Hawking method, we discuss the quantum Cosmology with O_(8N+1)^-symmetric coupling scalar field. The corresponding Wheeler-De Witt equation has been derived, and the wave function of the universe calculated. We got the material solution of the cosmic wave function in harmonic eigenstate, and the solution of space is the product of the Gauss factor and one polynomial. After analysing the wave function of the universe under the quantum effect, we found that the probability density of the universe appearing at a=0 is zero, and that the minimal radius of the ground state of the universe is on the Planck scale. The analysis of the wave function of the universe, also reveals that at the very early stage of the universe the probability density of the multl-scalar field is smaller than that of the onescalar field.

A comparison of phantom linear scalar field and non-linear Born-Infeld scalar field

This paper studies phantom linear scalar field （LSF） and phantom non-linear Born-Infeld （NLBI） scalar field with square potential of the form V（Ф） =1/2m^2Ф^2. The equation of state parameter w（z）, and evolution of scale factor a（t） in both phantom LSF and phantom NLBI scalar model are explored. The age of universe Hot and the transition redshift Z are obtained. The Gold data set of 157-SN-Ia is used to constrain parameters of the two models by numerical calculation. The phantom LSF is slightly better than the phantom NLBI type scalar field model for a large m. Although a smaller m corresponding to a slower rolling of field Ф better fits the observation data, the difference between phantom NLBI scalar field and phantom LSF is not distinct in this case.

Noise-Induced Origin of the Fundamental Scalar Field

The physical nature of the fundamental scalar field generation and hence the origination of the Universe is a matter of the discussions for many years. We propose to use the statistical approach to the description of the steady states of the quasi stationary systems with the elements of the quantum field theory methods as a basis to explain the appearance of the cosmological scalar field. Particularly, we apply two fundamental principles, i.e., the H-theorem and least-energy principle to show principal possibility of the scalar field origination. Along with the basic statement that in the presence of the fundamental scalar field, the energy of the vacuum ground state is lower than the ground state energy of the vacuum with no scalar field (primary vacuum), and with regard to the nonlinear interaction of fluctuating physical fields with the scalar field, these principles are employed to reveal probable phase transitions that may be associated with origin and further evolution of the Universe. Thus, we propose the possible physical justification of the spontaneous cosmological scalar field generation.

Tilted Bianchi Type VI0 Cosmological Model in Saez and Ballester Scalar Tensor Theory of Gravitation

Tilted Bianchi type VI0 cosmological model is investigated in a new scalar tensor theory of gravitation pro-posed by Saez and Ballester (Physics Letters A 113:467, 1986). Exact solutions to the field equations are derived when the metric potentials are functions of cosmic time only. Some physical and geometrical proper-ties of the solutions are also discussed.

Constraints on Dynamical Dark Energy with Precision Cosmological Data

We present a Dark Energy (DE) model based on a scalar field with an inverse power law potential (IPL) V(∅)=M4+n∅−n. We consider three different models n=1/2, n=3/4 and n=1 and we vary the value of M and the initial amount of energy density Ω∅at the scale factor ac. We obtain a time dependent equation of state (EoS) , with w∅=1/3 at early times for a scale factor ac with a steep transition to w∅=1 at , , , lasting a long period of time and a subsequent descent w∅=-1 to for to finally grow to w∅= -0.906, w∅=-0.932, w∅=-0.924 for n=1/2, n=3/4 and n=1 respectively. The values of M and Ω∅(ac) are M(eV)= 4.63,127.31,2465.46 and Ω∅(ac)=0.038,0.148,0.227 for n= 1/2, n= 3/4 and n=1 respectively. We show the differences in the evolution of H, the CMB and Matter power spectra, and the redshift space distortion (RSD)parameter. Precision cosmological data allow us to test the dynamics of Dark Energy and we obtain in all three cases a reduction of ?compared to ∧CDM with and an equivalent fit for CMB and SNIa data.

Estimations of cosmological parameters from the observational variation of the fine structure constant

We present constraints on the quintessence scalar field model from observational data of the variation of the fine structure constant obtained from the Keck telescope and VLT. Within the theoretical frame proposed by Bekenstein, the constraints on the parameters of the quintessence scalar field model are obtained. Considering the prior of Ωm0 as WMAP 7 suggests, we obtain various results from different sam- ples. Based on these results, we also calculate the probability density function of the coupling constant ζ. The best-fit values show a consistent relationship between ζ and the different experimental results. In our work, we test two different potential models, namely, the inverse power law potential and the exponential potential. The results show that both the large value of the parameters in the potential and the strong coupling can cause a variation in the fine structure constant.

Interaction of Gravitational field and Brans-Dicke field in R/W universe containing Dark Energy like fluid

On studying some new models of Robertson-Walker universes with a Brans-Dicke scalar field, it is found that most of these universes contain a dark energy like fluid which confirms the present scenario of the expansion of the universe. In one of the cases, the exact solution of the field equations gives a universe with a false vacuum, while in another it reduces to that of dust distribution in the Brans-Dicke cosmology when the cosmological constant is not in the picture. In one particular model it is found that the universe may undergo a Big Rip in the future, and thus it will be very interesting to investigate such models further.

Cosmological twinlike models with multi scalar fields

In this study, we consider cosmological models driven by several canonical or noncanonical scalar fields, and we show the manner in which twinlike models for a canonical model can be constructed from noncanonical ones using the superpotential method. We conclude that it is possible to construct twinlike models for multifield cosmological models, even with a nonzero spatial curvature.This work extends the discussions of [D. Bazeia, and J. D. Dantas, Phys. Rev. D 85, 067303(2012)] to cases with multi scalar fields and with non-vanished spatial curvature, by using a different superpotential method.

Reconstruction of Scalar Field Dark Energy Models in Kaluza-Klein Universe

This paper is devoted to study the modified holographic dark energy model by taking its different aspects in the t/at Kaiuza-Klein universe. We construct the equation of state parameter which evolutes the universe from quintessence region towards the vacuum. It is found that the modified holographic model exhibits instability against small perturbations in the early epoch of the universe but becomes stable in the later times. We also develop its correspondence with some scalar field dark energy models. It is interesting to mention here that ail the results are consistent with the present observations.

求Brans-Dicke理论中宇宙学解的一种简便方法

本文给出了一种比较简便的方法来处理标量一张量引力理论中 Brans-Dicke 场方程宇宙学模型的求解问题。利用这种方法,原先求解方法中必需分别处理的一个积分常数的三种不同值的情况,现在可以统一处理,并且得到的宇宙学解也可以表示为统一的形式。

追踪场中宇宙学参量的演化

考虑的宇宙模型为在平坦空间的Friedmann-Robertson-Walker(FRW)宇宙,且宇宙中仅包含具有指数势的标量场与具有正压的暗物质的两种流体;较为详细地数值研究了在宇宙的追踪演化过程中,各个宇宙学参量随标度因子变化的规律,得到的结果不仅与目前观测结果相一致,而且还有助于理解在追踪下各个宇宙学参量的演化行为.

非线性标量场为物质场的宇宙模型

宇宙的奇性问题始终是研究Einstein方程解的一个很重要的问题.根据Einstein场方程,在一个充满玻思-英费尔德非线性标量场为物质场的宇宙中,我们发现当非线性标量场的参量λ>0时,有一个有奇性的宇宙模型解;当参量λ<0时,有一个非奇性的宇宙模型解.

Vilenkin理论中具有共形标量场的量子宇宙学

本文利用Vilenkin的方法讨论了具有共形标量场的量子宇宙学.导出了相应的Whee-ler-DeWitt方程,计算了宇宙波函数.所得到的字宙波函数的物质部分解具有谐振子本征态的形式,空间部分的解是由WKB方法给出的.通过对宇宙波函数的分析发现考虑了量子效应后,宇宙在α=O处出现的几率密度为零,而宇宙基态最可几半径为Planck长度.由宇宙波函数的分析,还发现宇宙最可能处在较小的Φ值状态.

非平宇宙中的全息精质模型

提出了非平宇宙中的全息精质模型,构造出精质标量场,对全息暗能量的宇宙学演化进行有效描述.推导了全息暗能量在非平宇宙中的演化方程,进一步通过与正则标量场建立对应,构造出全息精质标量场模型,并讨论了空间曲率对模型的影响.结果表明,空间曲率对标量场演化的影响主要表现在高红移区域,而对于重构出的标量场势函数,在标量场值越小的区域空间曲率的影响越大.

Dynamics of scalar fields in an expanding/contracting cosmos at finite temperature

This study extends the investigation of quantum dissipative effects of a cosmological scalar field by taking into account cosmic expansion and contraction.Cheung,Drewes,Kang,and Kim calculated the effective action and quantum dissipative effects of a cosmological scalar field in a recent work,where analytical expressions for the effective potential and damping coefficient were presented using a simple scalar model with quartic interactions,and the work was conducted using Minkowski-space propagators in loop diagrams.In this work,we incorporate the Hubble expansion and contraction of the cosmic background and focus on the thermal dynamics of a scalar field in a regime where the effective potential changes slowly.Given that the Hubble parameter,H,attains a small but non-zero value,we carry out calculations to the first order in H.If we set H=0,all results match those in flat spacetime.Interestingly,we must integrate over the resonances,which in turn leads to an amplification of the effects of a non-zero H.This is an intriguing phenomenon,which cannot be uncovered in flat spacetime.The implications on particle creations in the early universe will be studied in a forthcoming study.

Multi-pole dark energy

A scalar field with a pole in its kinetic term is often used to study cosmological inflation;it can also play the role of dark energy,which is called the pole dark energy model.We propose a generalized model where the scalar field may have two or even multiple poles in the kinetic term,and we call it the multi-pole dark energy.We find that the poles can place some restrictions on the values of the original scalar field with a non-canonical kinetic term.After the transformation to the canonical form,we get a flat potential for the transformed scalar field even if the original field has a steep one.The late-time evolution of the universe is obtained explicitly for the two pole model,while dynamical analysis is performed for the multiple pole model.We find that it does have a stable attractor solution,which corresponds to the universe dominated by the potential of the scalar field.