Friedmann–Lemaître–Robertson–Walker metric

About: Friedmann–Lemaître–Robertson–Walker metric is a research topic. Over the lifetime, 4113 publications have been published within this topic receiving 87752 citations. The topic is also known as: FLRW metric.

Chameleonic Generalized Brans–Dicke model and late-time acceleration

Abstract: In this paper we consider Chameleonic Generalized Brans–Dicke Cosmology in the framework of FRW universes. The bouncing solution and phantom crossing is investigated for the model. Two independent cosmological tests: Cosmological Redshift Drift (CRD) and distance modulus are applied to test the model with the observation.

Cosmological milestones and energy conditions

Abstract: Until recently, the physically relevant singularities occurring in FRW cosmologies had traditionally been thought to be limited to the big bang, and possibly a big crunch. However, over the last few years, the zoo of cosmological singularities considered in the literature has become considerably more extensive, with big rips and sudden singularities added to the mix, as well as renewed interest in non-singular cosmological events such as bounces and turnarounds. In this talk, we present an extensive catalogue of such cosmological milestones, both at the kinematical and dynamical level. First, using generalized power series, purely kinematical definitions of these cosmological events are provided in terms of the behaviour of the scale factor a(t). The notion of a scale-factor singularity is defined, and its relation to curvature singularities (polynomial and differential) is explored. Second, dynamical information is extracted by using the Friedmann equations (without assuming even the existence of any equation of state) to place constraints on whether or not the classical energy conditions are satisfied at the cosmological milestones. Since the classification is extremely general, and modulo certain technical assumptions complete, the corresponding results are to a high degree model-independent.

Fluid dynamics in higher order gravity

Abstract: We examine the kinematic and dynamic properties of fluid spacetimes in higher order gravity. In particular we extend the general equations of Ehlers and Ellis governing relativistic fluid dynamics from general relativity to the higher order theory. We find exact results for the evolution of shear in Bianchi spacetimes with isotropic surfaces, thus generalising the general relativity results. Furthermore we show that the vanishing of vorticity, shear and acceleration does not imply FRW geometry inR + αR2 gravity without the further assumption of a barotropic equation of state,p = p(p), p′(p) ⊋ 0. In particular, this result means that the Ehlers-Geren-Sachs theorem on cosmic background radiation also holds in the higher order theory.

Bouncing universe and phantom crossing in modified gravity and its reconstruction

Abstract: In this paper we consider FRW cosmology in modified gravity which contains arbitrary functions f(ϕ). It is shown that the bouncing solution appears in the model whereas the equation of state (EoS) parameter crosses the phantom divider. The reconstruction of the model is also investigated with the aim to reconstruct the arbitrary functions and variables of the model.

Back reaction of the neutrino field in an Einstein universe

Abstract: The back-reaction effect of the neutrino field at finite temperature in the background of the static Einstein universe is investigated. A relationship between the temperature of the universe and its radius is found. As in previously studied cases of the massless scalar field and the photon field, this relation exhibits a minimum radius below which no self-consistent solution for the Einstein field equation can be found. A maximum temperature marks the transition from a vacuum-dominated state to the radiation-dominated state universe. In light of the results obtained for the scalar, neutrino and photon fields, the role of the back reaction of quantum fields in controlling the value of the cosmological constant is briefly discussed.