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.

Constraining Cosmological Parameters in the FLRW Metric with Lensed GW+EM Signals

Abstract: We proposed a model-independent method to constrain cosmological parameters using the Distance Sum Rule of the Friedmann–Lemaitre–Robertson–Walker metric by combining the time delay distances and the comoving distances through a multi-messenger approach. The time delay distances are measured from lensed gravitational wave (GW) signals together with their corresponding electromagnetic wave (EM) counterparts, while the comoving distances are obtained from a parameterized fitting approach with independent supernova observations. With a series of simulations based on the Einstein Telescope, Large Synoptic Survey Telescope, and The Dark Energy Survey, we find that only 10 lensed GW+EM systems can achieve the constraining power comparable to and even stronger than 300 lensed quasar systems due to the more precise time delay from lensed GW signals. Specifically, the cosmological parameters can be constrained to and (1σ).5 Our results show that more precise time delay measurements could provide more stringent cosmological parameter values, and lensed GW+EM systems therefore can be applied as a powerful tool in the future precision cosmology.

Isotropic and anisotropic N-dimensional cosmologies with exponential potentials

Abstract: We investigate (N + 1)-dimensional anisotropic cosmological models with a massless scalar field, self-interacting through an exponential potential. The problem is reduced to an FRW model with an additional free, massless scalar field. In the case we find the exact general solution for the Robertson-Walker spacetime and the N>3 anisotropic Bianchi type I model which is a product of a flat (3 + 1)-dimensional manifold and an (N - 3)-dimensional torus. In both cases the solutions present singularities and power-law inflation. In the multidimensional anisotropic case we also analyse the conditions under which dimensional reduction can proceed. When N = 1 we consider the gravitational theory formed by setting the Ricci scalar equal to the trace of the energy-momentum tensor of the matter fields. In this case the exact general solution of the second-order system of gravitational and self-interacting scalar field equations exhibit singularities, their most notable departure from the case being the absence of both particle horizons and power-law inflationary solutions.

Fixed points and FLRW cosmologies: Flat case

Abstract: We use phase space method to study possible consequences of fixed points in flat FLRW models. One of these consequences is that a fluid with a finite sound speed, or a differentiable pressure, reaches a fixed point in an infinite time and has no finite-time singularities of types I, II and III described in hep-th/0501025. It is impossible for such a fluid to cross the phantom divide in a finite time. We show that a divergent $dp/dH$, or a speed of sound is necessary but not sufficient condition for phantom crossing. We use pressure properties, such as asymptotic behavior and fixed points, to qualitatively describe the entire behavior of a solution in flat FLRW models. We discuss FLRW models with bulk viscosity $\eta \sim \rho^r$, in particular, solutions for $r=1$ and $r=1/4$ cases, which can be expressed in terms of Lambert-W function. The last solution behaves either as a nonsingular phantom fluid or a unified dark fluid. Using causality and stability constraints, we show that the universe must end as a de Sitter space. Relaxing the stability constraint leads to a de Sitter universe, an empty universe, or a turnaround solution that reaches a maximum size, then recollapses.

Cosmology of intersecting brane-world models in Gauss–Bonnet gravity

Abstract: We study the cosmological properties of a codimension two brane world that sits at the intersection between two four-branes, in the framework of six-dimensional Einstein–Gauss–Bonnet gravity. Due to contributions of the Gauss–Bonnet terms, the junction conditions require the presence of localized energy density on the codimension two defect. The induced metric on this surface assumes a FRW form, with a scale factor associated with the position of the brane in the background; we can embed in the codimension two defect the preferred form of energy density. We present the cosmological evolution equations for the three-brane, showing that, for the case of pure AdS6 backgrounds, they acquire the same form as the ones for the Randall–Sundrum II model. When the background is different from pure AdS6, the cosmological behaviour is potentially modified in respect to the typical one of codimension one brane worlds. We discuss, in a particular model embedded in an AdS6 black hole, the conditions one should satisfy in order to obtain standard cosmology at late epochs.

Elucidating cosmological model dependence with $H_0$

Abstract: We observe that the errors on the Hubble constant $$H_0$$ , a universal parameter in any FLRW cosmology, can be larger in specific cosmological models than Gaussian processes (GP) data reconstruction. We comment on the prior mean function and trace the smaller GP errors to stronger correlations, which we show precludes all well studied dynamical dark energy models. We also briefly illustrate cosmographic expansions as another model independent cosmological reconstruction. Our analysis suggests that “cosmological model independence”, especially in the statement of Hubble tension, has become a misnomer.