7. Mikko Lavinto, Syksy Rasanen, Sebastian J. Szybka Average expansion rate and light propagation in a cosmological Tardis spacetime JCAP, vol. 12, p. 051 (2013). [abstract] [preprint] [journal] [download] |
Abstract: We construct the first exact statistically homogeneous and isotropic cosmological solution in which inhomogeneity has a significant effect on the expansion rate. The universe is modelled as a Swiss Cheese, with Einstein-de Sitter background and inhomogeneous holes. We show that if the holes are described by the quasispherical Szekeres solution, their average expansion rate is close to the background under certain rather general conditions. We specialise to spherically symmetric holes and violate one of these conditions. As a result, the average expansion rate at late times grows relative to the background, i.e. backreaction is significant. The holes fit smoothly into the background, but are larger on the inside than a corresponding background domain: we call them Tardis regions. We study light propagation, find the effective equations of state and consider the relation of the spatially averaged expansion rate to the redshift and the angular diameter distance. |
8. Piotr T. Chru¶ciel, Christa R. Ölz, Sebastian J. Szybka Space-time diagrammatics Phys. Rev. D: Part. Fields , vol. 86, p. 124041 (2012). [abstract] [preprint] [journal] [download] |
Abstract: We introduce a new class of two-dimensional diagrams, the \emph{projection diagrams}, as a tool to visualize the global structure of space-times. We construct the diagrams for several metrics of interest, including the Kerr-Newman - (anti) de Sitter family, with or without cosmological constant, and the Emparan-Reall black rings. |
9. Piotr T. Chru¶ciel, Micha³ Eckstein, Luc Nguyen and Sebastian J. Szybka Existence of singularities in two-Kerr black holes Class. Quantum Grav., vol. 28, p. 245017 (2011). [abstract] [preprint] [journal] |
Abstract: We show that the angular momentum—area inequality 8π|J| ≤ A for weakly stable minimal surfaces would apply to I+-regular many-Kerr solutions, if any existed. Hence, we remove the undesirable hypothesis in the Hennig–Neugebauer proof of non-existence of well-behaved two-component solutions.
*supported by the grant from The John Templeton Foundation |
10. Piotr T. Chru¶ciel, Sebastian J. Szybka Stable causality of the Pomeransky-Senkov black holes Adv. Theor. Math. Phys., vol. 15, pp. 175-178 (2011). [abstract] [preprint] [journal] [download] |
Abstract: We show stable causality of the Pomeransky-Senkov black rings. |
11. Sebastian J. Szybka On light propagation in Swiss-Cheese cosmologies Phys. Rev. D: Part. Fields , vol. 84, p. 044011 (2011). [abstract] [preprint] [journal] [download] |
Abstract: We study the effect of inhomogeneities on light propagation. The Sachs equations are solved numerically in the Swiss-Cheese models with inhomogeneities modelled by the Lemaitre-Tolman solutions. Our results imply that, within the models we study, inhomogeneities may partially mimic the accelerated expansion of the Universe, but the effect is small. |
12. Sebastian J. Szybka Stable causality of Black Saturns Journal of High Energy Physics, vol. 2011, pp. 1-8 (2011). [abstract] [preprint] [journal] |
Abstract: We prove that the Black Saturns are stably causal on the closure of the domain of outer communications. |