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7. Szymon Sikora, Krzysztof Głód
Perturbatively constructed cosmological model with periodically distributed dust inhomogeneities
Phys. Rev. D: Part. Fields , vol. 99, p. 083512 (2019).
[abstract] [preprint] [journal]

We constructed a simple cosmological model which approximates the Einstein-de Sitter background with periodically distributed dust inhomogeneities. By taking the metric as a power series up to the third order in some perturbative parameter λ, we are able to achieve large values of the density contrast. With a metric explicitly given, many model properties can be calculated in a straightforward way which is interesting in the context of the current discussion concerning the averaging of the inhomogeneities and their backreaction in cosmology. Although the Einstein-de Sitter model can be thought of as the model average, the light propagation differs from that of Einstein-de Sitter. The angular diameter distance-redshift relation is affected by the presence of inhomogeneities and depends on the observer’s position. The model construction scheme enables some generalizations in the future, so the present work is a step toward more realistic cosmological model described by a relatively simple analytical metric.

8. Piotr T. Chruściel, Sebastian J. Szybka, Paul Tod
Towards a classification of vacuum near-horizons geometries
Class. Quantum Grav. 35 (2018) 015002, vol. 35, p. 015002 (2018).
[abstract] [preprint] [journal]

We prove uniqueness of the near-horizon geometries arising from degenerate Kerr black holes within the collection of nearby vacuum near-horizon geometries.

9. Szymon Sikora, Krzysztof Głód
Example of an inhomogeneous cosmological model in the context of backreaction
Phys. Rev. D: Part. Fields , vol. 95, p. 063517 (2017).
[abstract] [preprint] [journal]

In this article, we present an example of an inhomogeneous cosmological model, which is inspired by the linear perturbation theory. The metric of this model can be described as the Einstein–de Sitter background with periodically distributed dust overdensities. The model construction enables application of the Green-Wald averaging scheme and the Buchert averaging technique simultaneously. We compare the angular diameter distance function of the considered model to the angular diameter distances corresponding to the average space-times given by the Green-Wald and the Buchert frameworks respectively.

10. Editor: Sebastian J. Szybka
The 3rd Conference of the Polish Society on Relativity
Acta Physica Polonica B (2017), PL ISSN 1899-2358 [journal]


11. Sebastian J. Szybka, Michał J. Wyrȩbowski
Backreaction for Einstein-Rosen waves coupled to a massless scalar field
Phys. Rev. D: Part. Fields , vol. 94, p. 024059 (2016).
[abstract] [preprint] [journal]

We present a one-parameter family of exact solutions to Einstein's equations that may be used to study the nature of the Green-Wald backreaction framework. Our explicit example is a family of Einstein-Rosen waves coupled to a massless scalar field.

12. Sebastian J. Szybka
Równania Einsteina i efekt niejednorodności w kosmologii
W ,,Ogólna teoria względności a filozofia - sto lat interakcji'', red. P. Polak, J. Mączka, CCPress, pp. 127-142 [journal]


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