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 cosmology with numerical relativity

Abstract: We perform three-dimensional numerical relativity simulations of homogeneous and inhomogeneous expanding spacetimes, with a view towards quantifying non-linear effects from cosmological inhomogeneities. We demonstrate fourth-order convergence with errors less than one part in 10^6 in evolving a flat, dust Friedmann-Lemaitre-Roberston-Walker (FLRW) spacetime using the Einstein Toolkit within the Cactus framework. We also demonstrate agreement to within one part in 10^3 between the numerical relativity solution and the linear solution for density, velocity and metric perturbations in the Hubble flow over a factor of ~350 change in scale factor (redshift). We simulate the growth of linear perturbations into the non-linear regime, where effects such as gravitational slip and tensor perturbations appear. We therefore show that numerical relativity is a viable tool for investigating nonlinear effects in cosmology.

Unifying inflation with dark energy in modified F(R) Horava-Lifshitz gravity

Abstract: We study FRW cosmology for a non-linear modified F(R) Horava-Lifshitz gravity which has a viable convenient counterpart. A unified description of early-time inflation and late-time acceleration is possible in this theory, but the cosmological dynamic details are generically different from the ones of the convenient viable F(R) model. Remarkably, for some specific choice of parameters they do coincide. The emergence of finite-time future singularities is investigated in detail. It is shown that these singularities can be cured by adding an extra, higher-derivative term, which turns out to be qualitatively different when compared with the corresponding one of the convenient F(R) theory.

Quantization of a coupled Fermi field and Robertson-Walker metric

Abstract: The combined Dirac field and Robertson-Walker metric system is quantized in a Heisenberg picture. One of the Einstein equations is implemented as a constraint on the state vectors and leads to a spectrum for the allowed values of the mass of the spinor field.

Cosmological perturbations on a magnetized Bianchi I background

Abstract: Motivated by the isotropy of the CMB spectrum, all existing studies of magnetized cosmological perturbations employ FRW backgrounds However, it is important to know the limits of this approximation and the effects one loses by neglecting the anisotropy of the background magnetic field We develop a new treatment, which fully incorporates the anisotropic magnetic effects by allowing for a Bianchi I background universe The anisotropy of the unperturbed model facilitates the closer study of the coupling between magnetism and geometry The latter leads to a curvature stress, which accelerates positively curved perturbed regions and balances the effect of magnetic pressure gradients on matter condensations We argue that the tension carried along the magnetic force lines is the reason behind these magneto-curvature effects For a relatively weak field, we also compare with the results of the almost-FRW approach We find that some of the effects identified by the FRW treatment are in fact direction-dependent, where the key direction is that of the background magnetic field vector Nevertheless, the FRW-based approach to magnetized cosmological perturbations remains an accurate approximation, particularly on large scales, when one looks at the lowest-order magnetic impact on gravitational collapse On small scales, however, the accuracy of the perturbed Friedmann framework may be compromised by extra shear effects

The Large Number Hypothesis and Einstein's Theory of Gravitation

Abstract: In an attempt to reconcile the large number hypothesis (LNH) with Einstein's theory of gravitation, a tentative generalization of Einstein's field equations with time-dependent cosmological and gravitational constants is proposed. A cosmological model consistent with the LNH is deduced. The coupling formula of the cosmological constant with matter is found, and as a consequence, the time-dependent formulae of the cosmological constant and the mean matter density of the Universe at the present epoch are then found. Einstein's theory of gravitation, whether with a zero or nonzero cosmological constant, becomes a limiting case of the new generalized field equations after the early epoch.