1. Sebastian J. Szybka, Adam Cieślik On standing waves in general relativity , vol. xxx, pp. xxxxxx (2019). [abstract] [preprint] 
Abstract: We propose a covariant definition of standing gravitational waves in general relativity. 
2. Sebastian J. Szybka, Mieszko Rutkowski Einstein clusters as models of inhomogeneous spacetimes Journal, vol. xxx, pp. xxxxxx (2019). [abstract] [preprint] [journal] 
Abstract: We study the effect of smallscale inhomogeneities for Einstein clusters. We construct a spherically symmetric stationary spacetime with smallscale radial inhomogeneities and propose the Gedankenexperiment. An hypothetical observer at the center constructs, using limited observational knowledge, a simplified homogeneous model of the configuration. An idealization introduces tensions and side effects. The inhomogeneous spacetime and the effective homogeneous spacetime are given by exact solutions to Einstein equations. They provide a simple toymodel for studies of the effect of smallscale inhomogeneities in general relativity. 
3. 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] 
Abstract: We constructed a simple cosmological model which approximates the Einsteinde 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 Einsteinde Sitter model can be thought of as the model average, the light propagation differs from that of Einsteinde Sitter. The angular diameter distanceredshift 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. 
4. Piotr T. Chruściel, Sebastian J. Szybka, Paul Tod Towards a classification of vacuum nearhorizons geometries Class. Quantum Grav. 35 (2018) 015002, vol. 35, p. 015002 (2018). [abstract] [preprint] [journal] 
Abstract: We prove uniqueness of the nearhorizon geometries arising from degenerate Kerr black holes within the collection of nearby vacuum nearhorizon geometries. 
5. 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] 
Abstract: 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 GreenWald 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 spacetimes given by the GreenWald and the Buchert frameworks respectively. 
6. Editor: Sebastian J. Szybka The 3rd Conference of the Polish Society on Relativity Acta Physica Polonica B (2017), PL ISSN 18992358 [journal] 
Abstract:
