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.

Inhomogeneous viscous dark fluid coupled with dark matter in the FRW universe

Abstract: A cosmological model with an inhomogeneous viscous dark fluid coupled with dark matter in a flat Friedmann–Robertson–Walker (FRW) universe is investigated. The influence of dark matter on the behavior of an inhomogeneous viscous fluid of this kind, responsible for cosmic acceleration and for the appearance of different types of singularities, is analyzed in detail. In particular, the critical points corresponding to the solutions of the background equations in a useful approximation are obtained explicitly.

The generalized second law of gravitational thermodynamics on the apparent and event horizons in FRW cosmology

Abstract: We investigate the validity of the generalized second law of gravitational thermodynamics on the apparent and event horizons in a non-flat FRW universe containing the interacting dark energy with dark matter. We show that for the dynamical apparent horizon, the generalized second law is always satisfied throughout the history of the universe for any spatial curvature and it is independent of the equation of state parameter of the interacting dark energy model. Whereas for the cosmological event horizon, the validity of the generalized second law depends on the equation of state parameter of the model.

The Cosmological Spacetime

Abstract: We present here the transformations required to recast the Robertson-Walker metric and Friedmann-Robertson-Walker equations in terms of observer-dependent coordinates for several commonly assumed cosmologies. The overriding motivation is the derivation of explicit expressions for the radius R_h of our cosmic horizon in terms of measurable quantities for each of the cases we consider. We show that the cosmological time dt diverges for any finite interval ds associated with a process at R -> R_h, which therefore represents a physical limit to our observations. This is a key component required for a complete interpretation of the data, particularly as they pertain to the nature of dark energy. With these results, we affirm the conclusion drawn in our earlier work that the identification of dark energy as a cosmological constant does not appear to be consistent with the data.

Solution of Einstein's Field Equations for a Rotating, Stationary, and Dust‐Filled Universe

Abstract: The solution of Einstein's field equations, Rij−12gijR=8πκρuiuj+λgij, for a line element of the form ds2=(dx0)2−δ2(x1)(dx1)2+2β(x1)dx0dx2−γ2(x1)(dx2)−α2(x1)(dx3)2 is found. The density, ρ, may be a function of position, and the cosmological constant λ is not necessary in order to have a finite density. The solution reduces to that of Godel if the variable α is constant. If the requirement for an empty universe is made (Rij = 0), the solution is conformally flat. The characteristics of the conformal curvature tensor are also obtained.

Quasi-topological electromagnetism: Dark energy, dyonic black holes, stable photon spheres and hidden electromagnetic duality

Abstract: We introduce the quasi-topological electromagnetism which is defined to be the squared norm of the topological 4-form F ∧ F. A salient property is that its energy-momentum tensor is of the isotropic perfect fluid with the pressure being precisely the opposite to its energy density. It can thus provide a model for dark energy. We study its application in both black hole physics and cosmology. The quasi-topological term has no effect on the purely electric or magnetic Reissner-Nordstrom black holes, the dyonic solution is however completely modified. We find that the dyonic black holes can have four real horizons. For suitable parameters, the black hole can admit as many as three photon spheres, with one being stable. Another intriguing property is that although the quasi-topological term breaks the electromagnetic duality, the symmetry emerges in the on-shell action in the Wheeler-DeWitt patch. In cosmology, we demonstrate that the quasi-topological term alone is equivalent to a cosmological constant, but the model provides a mechanism for the dark energy to couple with other types of matter. We present a concrete example of the quasi-topological electromagnetism coupled to a scalar field that admits the standard FLRW cosmological solutions.