25. Sebastian J. Szybka
On light propagation in Swiss-Cheese cosmologies
Phys. Rev. D: Part. Fields , vol. 84, p. 044011 (2011).
[abstract] [preprint] [journal] [download]
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.
26. Sebastian J. Szybka
Stable causality of Black Saturns
Journal of High Energy Physics, vol. 2011, pp. 1-8 (2011).
[abstract] [preprint] [journal]
We prove that the Black Saturns are stably causal on the closure of the domain of outer communications.
27. Wojciech Czaja, Zdzislaw A. Golda, Andrzej Woszczyna
Consistent initial data for CMD perturbations
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.
28. Wojciech Czaja, Zdzislaw A. Golda, Andrzej Woszczyna
Momentum of cosmological acoustic field
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.
29. Wojciech Czaja, Zdzislaw A. Golda, Andrzej Woszczyna
The acoustic wave equation in the expanding universe. Sachs-Wolfe theorem
The Mathematica Journal, vol. 13 (2011).
[abstract] [journal] [cdf]
This article considers the acoustic field propagating in the radiation-dominated universe of arbitrary space curvature. The field equations are reduced to the d’Alembert equation in an auxiliary static Robertson-Walker spacetime and dispersion relations are discussed.
*supported by the grant from The John Templeton Foundation
30. Sebastian J. Szybka
Niektórzy twierdzą, że świat skończy się w lodzie - Nagroda Nobla z fizyki 2011
Foton, vol. 115, pp. 11-16 (2011).