On stability of Friedmann-Lemaître-Robertson-Walker solutions in doubled geometries

Intrinsic energy of Lemaître-Tolman-Bondi models and cosmological implications

Recently, some Lema{\^ı}tre-Tolman-Bondi metrics have been considered as models alternative to the dark energy within the Friedmann-Lema{\^ı}tre-Robertson-Walker universes. The vanishing of the intrinsic energy of these metrics is examined since such a vanishing, in the present case and in general, could be interpreted as a necessary condition to consider the possibility of the quantum creation of a metric. More specifically, this vanishing is examined in the particular case where the Lema{\^ı}tre-Tolman-Bondi metrics behave asymptotically like a Friedmann-Lema{\^ı}tre-Robertson-Walker univers…

轴向Bianchi IX模型及其Lemaître-Hubble图

Axial Bianchi IX and its Lema{î}tre-Hubble diagram

本研究基于宇宙学原理的最小对称性破缺标准，计算了含共动尘埃的轴向Bianchi IX宇宙的Lemaître-Hubble图，发现该标准仅允许轴向Bianchi I和正曲率的Bianchi IX宇宙，且排除了负曲率情形。

Repulsive regions in Lemaître-Tolman-Bondi gravitational collapse

We show that in the inhomogeneous Lema{î}tre-Tolman-Bondi space-time there are specific regions in which repulsive gravity exists. To find these regions, we use an invariant definition of repulsive gravity based upon the behavior of the curvature eigenvalues. In addition, we analyze the effects of repulsive gravity on the dynamics of the gravitational collapse. In particular, we investigate the collapse in the case of the parabolic solution for the effective scale factor of the Lema{î}tre-Tolman-Bondi metric, corresponding to the marginally bound case. Exploring the corresponding cut-offs at w…

Towards modified bimetric theories within non-product spectral geometry

We discuss class of doubled geometry models with diagonal metrics. Based on the analysis of known examples we formulate a hypothesis that supports treating them as modified bimetric gravity theories. Certain steps towards the generic case are then performed.

Cosmic censorship conjecture in some matching spherical collapsing metrics

A physically plausible Lema{\^ı}tre-Tolman-Bondi collapse in the marginally bound case is considered. By "physically plausible" we mean that the corresponding metric is ${\cal C}^1$ matched at the collapsing star surface and further that its {\em intrinsic} energy is, as due, stationary and finite. It is proved for this Lema{\^ı}tre-Tolman-Bondi collapse, for some parameter values, that its intrinsic central singularity is globally naked, thus violating the cosmic censorship conjecture with, for each direction, one photon, or perhaps a pencil of photons, leaving the singularity and reaching th…

Geodesic family of spherical instantons and cosmic quantum creation

The Einstein field equations for any spherically symmetric metric and a geodesic perfect fluid source are cast in a canonical simple form, both for Lorentzian metrics and for instantons. Both kinds of metrics are explicitly written for the Lema{\^ı}tre-Tolman-Bondi family and for a general $Λ$-Friedmann-Lema{\^ı}tre-Robertson-Walker universe. In the latter case (including of course the instanton version) we study whether the probability of quantum creation of our Universe vanishes or not. It is found, in accordance with previous results, that only the closed model can have a nonzero probabilit…