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.

On coincidence problem and attractor solutions in ELKO dark energy model

Abstract: We study the critical points of a Universe dominated by ELKOspinor field dark energy and a barotropic matter in an almost generalcase. The coincidence problem and attractor solutions are discussedand it is shown the coincidence problem can not be alleviated in thismodel.PACS numbers: 95.36.+x, 95.35.+d, 98.80.-k 1 Introduction To describe the present accelerated expansion of the universe [1], manymodels have been considered. In dark energy models, almost 70% of ouruniverse is assumed to be filled with a smooth unknown matter with negativepressure known as dark energy. Although the first candidates proposedfor dark energy were exotic dynamical scalar field such as quintessence orphantom, but, spinor dark energy model has also attracted some attentionsrecently [2].In [3], a class of non standard spinors, constructed in momentum spacefrom the eigenspinors of the charge conjugation operator, known as ELKOspinor(EigenspinorendesLadungsKonjugationsOperators), satisfying (CPT) 2 =−1, was introduced. Cosmological consequences of this model in a spatiallyflat Friedmann Robertson Walker (FRW) space-time were studied in [4].However viable modelsmust beconsistent with astrophysical data. Thesedata indicate that, despite the expansion of the universe, the ratio of matterto dark energy density is of order r:=

Bouncing and emergent cosmologies from ADM RG flows

Abstract: The Asymptotically Safe Gravity provides a framework for the description of gravity from the trans-Planckian regime to cosmological scales. According to this scenario, the cosmological constant and Newton's coupling are functions of the energy scale whose evolution is dictated by the renormalization group equations. The formulation of the renormalization group equations on foliated spacetimes, based on the Arnowitt-Deser-Misner (ADM) formalism, furnishes a natural way to construct the RG energy scale from the spectrum of the laplacian operator on the spatial slices. Combining this idea with a Renormalization Group improvement procedure, in this work we study quantum gravitational corrections to the Einstein-Hilbert action on Friedmann-Lemaitre-Robertson-Walker (FLRW) backgrounds. The resulting quantum-corrected Friedmann equations can give rise to both bouncing cosmologies and emergent universe solutions. Our bouncing models do not require the presence of exotic matter and emergent universe solutions can be constructed for any allowed topology of the spatial slices.

Hyperboloidal initial data for the vacuum Einstein equations with cosmological constant

Abstract: The existence of smooth hyperboloidal initial data sets for the vacuum Einstein equations with non-zero cosmological constant is studied. Supposing that the trace of the (physical) second fundamental form of the initial hypersurface is constant, there is a correspondence between the solutions of the vacuum constraints with and without cosmological constant, respectively. This enables us to extend the results proved by Andersson and Chrusciel about the smoothness of the initial data with zero cosmological constant to the case .

Parity violating Friedmann Universes

Abstract: We revisit extensions of the Einstein-Cartan theory where the cosmological constant $\mathrm{\ensuremath{\Lambda}}$ is promoted to a variable, at the cost of allowing for torsion even in the absence of spinors. We remark that some standard notions about Friedmann-Robertson-Walker (FRW) universes collapse in these theories, most notably that spatial homogeneity and isotropy may now coexist with violations of parity invariance. The parity-violating solutions have nonvanishing Weyl curvature even within FRW models. The presence of parity-violating torsion opens up the space of possible such theories with relevant FRW modifications; in particular the Pontryagin term can play an important role even in the absence of spinorial matter. We present a number of parity-violating solutions with and without matter. The former are the non-self-dual vacuum solutions long suspected to exist. The latter lead to tracking and nontracking solutions with a number of observational problems, unless we invoke the Pontryagin term. An examination of the Hamiltonian structure of the theory reveals that the parity-even and the parity-violating solutions belong to two distinct branches of the theory, with different gauge symmetries (constraints) and different numbers of degrees of freedom (d.o.f.). The parity-even branch is nothing but standard relativity with a cosmological constant which has become pure gauge under conformal invariance if matter is absent, or a slave of matter (and so not an independent d.o.f.) if nonconformally invariant matter is present. In contrast, the parity-violating branch contains a genuinely new d.o.f.

Black Hole in the Expanding Universe with Arbitrary Power-Law Expansion

Abstract: We present a time-dependent and spatially inhomogeneous solution that interpolates the extremal Reissner-Nordstroem (RN) black hole and the Friedmann-Lemaitre-Robertson-Walker (FLRW) universe with arbitrary power-law expansion. It is an exact solution of the D-dimensional Einstein-Maxwell-dilaton system, where two Abelian gauge fields couple to the dilaton with different coupling constants, and the dilaton field has a Liouville-type exponential potential. It is shown that the system satisfies the weak energy condition. The solution involves two harmonic functions on a (D-1)-dimensional Ricci-flat base space. In the case where the harmonics have a single-point source on the Euclidean space, we find that the spacetime describes a spherically symmetric charged black hole in the FLRW universe, which is characterized by three parameters: the steepness parameter of the dilaton potential n{sub T}, the U(1) charge Q, and the nonextremality {tau}. In contrast with the extremal RN solution, the spacetime admits a nondegenerate Killing horizon unless these parameters are finely tuned. The global spacetime structures are discussed in detail.