19. 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 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.

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

Abstract:

21. Jałocha J., Bratek Ł., Pękala J., Sikora S., Kutschera M.
Magnetic flux density from the relative circular motion of stars and partially ionized gas in the Galaxy mid-plane vicinity
Astrophys J. , vol. 833, p. 174 (2016).
[abstract] [preprint] [journal]

Abstract:
Observations suggest a slower stellar rotation relative to gas rotation in the outer part of the Milky Way Galaxy. This difference could be attributed to an interaction with the interstellar magnetic field. In a simple model, fields of order 10 micro Gauss are then required, consistently with the observed values. This coincidence suggests a tool for estimating magnetic fields in spiral galaxies. A North-South asymmetry in the rotation of gas in the Galaxy could be of magnetic origin too.

22. 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]

Abstract:
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.

23. 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]

Abstract:

24. Bratek Ł., Sikora S., Jałocha J., Kutschera M.
Velocity-density twin transforms in the thin disk model
Mon. Not. R. Astron. Soc. , vol. 451, p. 4018 (2015).
[abstract] [preprint] [journal]

Abstract:
Ring mass density and the corresponding circular velocity in thin disc model are known to be integral transforms of one another. But it may be less familiar that the transforms can be reduced to one-fold integrals with identical weight functions. It may be of practical value that the integral for the surface density does not involve the velocity derivative, unlike the equivalent and widely known Toomre's formula.