Black Holes in the Universe: Generalized Lemaitre-Tolman-Bondi Solutions

We present new exact solutions {which presumably describe} black holes in the background of a spatially flat, pressureless dark matter (DM)-, or dark matter plus dark energy (DM+DE)-, or quintom-dominated universe. These solutions generalize Lemaitre-Tolman-Bondi metrics. For a DM- or (DM+DE)-dominated universe, the area of the black hole apparent horizon (AH) decreases with the expansion of the universe while that of the cosmic AH increases. However, for a quintom-dominated universe, the black hole AH first shrinks and then expands, while the cosmic AH first expands and then shrinks. A (DM+DE)-dominated universe containing a black hole will evolve to the Schwarzschild-de Sitter solution with both AHs approaching constant size. In a quintom-dominated universe, the black hole and cosmic AHs will coincide at a certain time, after which the singularity becomes naked, violating Cosmic Censorship.Comment: 13 pages, 4 figure

Leptogenesis from N~\widetilde{N}-dominated early universe

We investigate in detail the leptogenesis by the decay of coherent right-handed sneutrino $\widetilde{N}$ having dominated the energy density of the early universe, which was originally proposed by HM and TY. Once the $\widetilde{N}$ dominant universe is realized, the amount of the generated lepton asymmetry (and hence baryon asymmetry) is determined only by the properties of the right-handed neutrino, regardless of the history before it dominates the universe. Moreover, thanks to the entropy production by the decay of the right-handed sneutrino, thermally produced relics are sufficiently diluted. In particular, the cosmological gravitino problem can be avoided even when the reheating temperature of the inflation is higher than 10^{10}\GeV, in a wide range of the gravitino mass m_{3/2}\simeq 10\MeV--100\TeV. If the gravitino mass is in the range m_{3/2}\simeq 10\MeV--1\GeV as in the some gauge-mediated supersymmetry breaking models, the dark matter in our universe can be dominantly composed of the gravitino. Quantum fluctuation of the $\widetilde{N}$ during inflation causes an isocurvature fluctuation which may be detectable in the future.Comment: 16 page

Velocity dominated singularities in the cheese slice universe

We investigate the properties of spacetimes resulting from matching together exact solutions using the Darmois matching conditions. In particular we focus on the asymptotically velocity term dominated property (AVTD). We propose a criterion that can be used to test if a spacetime constructed from a matching can be considered AVTD. Using the Cheese Slice universe as an example, we show that a spacetime constructed from a such a matching can inherit the AVTD property from the original spacetimes. Furthermore the singularity resulting from this particular matching is an AVTD singularity.Comment: 11 pages, 3 figures, accepted for publication in the International Journal of Modern Physics

Frozen rigging model of the energy dominated universe

Composite rigging systems, involving membranes that meet on strings that meet on monopoles, arise naturally by the Kibble mechanism as topological defects in field theories involving spontaneous symmetry breaking. Such systems will tend to freeze out into static lattice type configurations with energy contribution ultimately be provided by the membranes. It has been suggested by Bucher and Spergel that on scales large compared with the relevant (interstellar separation) distance characterising the relevant mesh length, such a system may behave as a rigidity - stabilised solid, having an approximately isotropic stress energy tensor with negative pressure, as given by a polytropic index $\gamma=w+1=1/3$. It has recently been shown that such a system can be rigid enough to be stable if the number of membranes meeting at a junction is even (though not if it is odd). Using as examples an approximately O(3) symmetric scalar field model that can provide an ``8 color'' (body centered) cubic lattice, and an approximate U(1)$\times$ U(1) model offering a disordered ``5 color'' lattice, it is argued that such a mechanism can account naturally for the observed dark energy dominance of the universe, without ad hoc assumptions, other than that the relevant symmetry breaking phase transition should have occurred somewhere about the Kev energy range.Comment: 14 pages, LaTex. Contrib. to Micro and Macro Structures of Spacetime, Peyresq, June, 2004, extended to include illustrations of "8 color" and "5 color" examples of "even" (as opposed to "odd") lattice