Department of Relativistic Astrophysics and Cosmology
 
 
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25. 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

26. 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.

27. 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.

28. 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.

29. Wojciech Czaja, Zdzislaw A. Golda, Andrzej Woszczyna
Consistent initial data for CMD perturbations
(2011).
[abstract] [preprint]

Abstract:
We investigate the initial condition which are simultaneously consistent with perturbation equations in both the radiation-dominated and the mater-dominated epochs. The exact formula for the spectrum transfer-function is derived.

30. Wojciech Czaja, Zdzislaw A. Golda, Andrzej Woszczyna
Momentum of cosmological acoustic field
(2011).
[abstract] [preprint]

Abstract:
The acoustic spacetime corresponding to perturbed Friedman-Lemaitre-Robertson-Walker universe inherit the space isometries from the original FLRW model, but essentially differs in dynamics. The scale factor manifestly depends on the equation of state of the matter content. Despite the higher complexity of the background evolution the perturbation equation in this space is substantially simpler: the density perturbations obey d'Alembert equation. Canonical formalism reconstructed in the acoustic spacetime enables one to employ the Klein-Gordon scalar product. Consequently, the Fourier decomposition of the perturbation field provide the time-independent Fourier coefficients and the time-independent spectrum. The perturbation spectrum does not depend of the choice of the Cauchy hypersurface from which the data are collected. Noether constants associated with the six-parameter isometry group define the components of the momentum, hyperbolic momentum and angular momentum of sound.

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