In a previous work [S. Rahbardehghan et al. in Phys. Lett. B 750, 627 (2015)], we considered a simple brane-world model; a single $4$-dimensional brane embedded in a $5$-dimensional de Sitter (dS) space-time. Then, by including a conformally coupled scalar field in the bulk, we studied the induced Casimir energy-momentum tensor. Technically, the Krein-Gupta-Bleuler (KGB) quantization scheme as a covariant and renormalizable quantum field theory in dS space was used to perform the calculations. In the present paper, we generalize this study to a less idealized, but physically motivated, scenario, namely we consider Friedmann-Robertson-Walker (FRW) space-time which behaves asymptotically as a dS space-time. More precisely, we evaluate Casimir energy-momentum tensor for a system with two $D$-dimensional curved branes on background of $D+1$-dimensional FRW space-time with negative spatial curvature and a conformally coupled bulk scalar field that satisfies Dirichlet boundary condition on the branes.
A regularization procedure has been recently suggested for regularizing Big Bang singularities in Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetimes. We argue that this procedure is only appliable to one case of Big Bang singularities and does not affect other types of singularities.
Hawking's proposal that the Universe has no temporal boundary and hence no beginning depends on the notion of imaginary time and is usually referred to as the "no-boundary proposal." This paper discusses a simple alternative approach by means of the five-dimensional Friedmann-Lemaitre-Robertson-Walker model.
A global intrinsic time in Friedmann - Robertson - Walker models is proportional to a scaling factor of the spatial metric. The aim of the paper is to study an applicability of the intrinsic global time chosen to nearest non-symmetric cases by taking into account linear metric perturbations. Scalar linear perturbations add some corrections to the effective energy density in the Hubble law. The metric vector and tensor perturbations in linear approximation do not influence the intrinsic time.
Global existence of solutions for the Einstein-Boltzmann system with cosmological constant in the Robertson-Walker space-time for arbitrarily large initial data
We investigate toroidal Marginally Outer Trapped Surfaces (MOTS) and Marginally Outer Trapped Tubes (MOTT) in closed Friedmann-Lemaitre-Robertson-Walker (FLRW) geometries. They are constructed by embedding Constant Mean Curvature (CMC) Clifford tori in a FLRW spacetime. This construction is used to assess the quality of certain isoperimetric inequalities, recently proved in axial symmetry. Similarly to spherically symmetric MOTS existing in FLRW spacetimes, the toroidal ones are also unstable.
In this letter we summarize our analysis of Bose-Einstein condensation on closed Robertson-Walker spacetimes. In a previous work we defined an adiabatic KMS state on the Weyl-algebra of the free massive Klein-Gordon field. This state describes a free Bose gas on Robertson-Walker spacetimes. We use this state to analyze the possibility of Bose-Einstein condensation on closed Robertson-Walker spacetimes. We take into account the effects due to the finiteness of the spatial volume and show that they are not relevant in the early universe. Furthermore we show that a critical radius can be defined.…
We study the cosmological evolution with nonsingular branes generated by a bulk scalar field coupled to gravity. The specific setup investigated leads to branes with a time-dependent warp factor. We calculate the effective Hubble parameter and the effective scale factor for the FRW branes obtained solutions. The spatially dependent branes solutions also were found.
In this paper, we consider the Cauchy problem for the relativistic Boltzmann equation with near vacuum initial data where the distribution function depends on the time, the position and the impulsion. The collision kernel considered here is for the hard potentials case and the background space-time in which the study is done is the Robertson-Walker space-time. Unique global (in time) mild solution is obtained in a suitable weighted space.
Friedmann-Robertson-Walker like cosmologies with spherical symmetry
我们重新考虑了金成元[Phys. Rev D 53，6889（1996）]在具有可穿越虫洞的弗里德曼-罗伯逊-沃克宇宙学的背景下讨论的宇宙学模型，其中假设物质内容分为两部分：仅依赖于时间的宇宙部分和仅依赖于空间的虫洞部分。宇宙部分服从正压状态方程$p_c=γρ_c$。完整的分析需要进一步的关注，并揭示了比作者以前所展示的更有趣的结果。它们可以很容易地应用到一大类宇宙学模型的演化，这是更普遍的比FRW模型。
We apply a new global dynamical systems formulation to flat Robertson-Walker cosmologies with a massless and massive Yang-Mills field and a perfect-fluid with linear equation of state as the matter sources. This allows us to give proofs concerning the global dynamics of the models including asymptotic source-dominance towards the past and future time directions. For the pure massless Yang-Mills field, we also contextualize well-known explicit solutions in a global (compact) state space picture.
In the present paper, we are considering a spatially-flat Friedmann-Robertson-Walker cosmological model, fueled with stiff matter and dust, treated as non-interacting ideal fluid sources. By solving the corresponding Friedmann equation with a non-zero cosmological constant, we are deriving the scale function and the fundamental cosmological parameters. Within a thermodynamic approach, the general form of the Equation of State is obtained, together with the explicit dependence of the energy density and pressure on temperature.
Phase-plane analysis of Friedmann-Robertson-Walker cosmologies in Brans-Dicke gravity
我们提出了一个自治的相平面描述的Friedmann-Robertson-Walker模型包含一个完美的流体（正压指数γ）在Brans-Dicke引力（Brans-Dicke参数ω）的演变。我们发现自相似不动点对应于纳里埃的幂律解决方案的空间平坦的模型和曲率缩放的解决方案弯曲的模型。在无限值的相平面变量，我们恢复O 'Hanlon和Tupper的真空解决方案的空间平坦的模型和米尔恩宇宙的负空间曲率。我们发现这些临界点的存在性和稳定性的条件，并描述在所有区域的（Ω，伽马）参数空间0<伽马-3/2的定性演变<2 and omega>。我们证明了在Brans-Dicke引力中暴胀的条件总是强于广义相对论的条件，γ <2/3。
