1. 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. |
2. Editor: Sebastian J. Szybka The 3rd Conference of the Polish Society on Relativity Acta Physica Polonica B (2017), PL ISSN 1899-2358 [journal] |
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3. 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. |
4. 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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5. Nicolas Franco, Michał Eckstein Causality in noncommutative two-sheeted space-times , vol. xxx, pp. xxx-xxx (2015). [abstract] [preprint] |
Abstract: We investigate the causal structure of two-sheeted space-times using the tools of Lorentzian spectral triples. We show that the noncommutative geometry of these spaces allows for causal relations between the two sheets. The computation is given in details when the sheet is a 2- or 4-dimensional globally hyperbolic spin manifold. The conclusions are then generalised to a point-dependent distance between the two sheets resulting from the fluctuations of the Dirac operator. |
6. Michał Eckstein, Nicolas Franco Causal structure for noncommutative geometry Frontiers of Fundamental Physics, vol. 14, pp. 138-xxx (2015). [abstract] [journal] |
Abstract: Noncommutative Geometry à la Connes offers a promising framework for models of fundamental interactions. To guarantee the correct signature, the theory of Lorentzian spectral triples has been developed. We will briefly summarise its main elements and show that it can accommodate a sensible notion of causality understood as a partial order relation on the space of states on an algebra. For almost-commutative algebras of the form $C^\infty \otimes \A_F$, with $\A_F$ being finite-dimensional, the space of (pure) states is a simple product of space-time $\M$ and an internal space. The exploration of causal structures in this context leads to a surprising conclusion: The motion in both space-time and internal space is restricted by a "finite speed of light" constraint. We will present this phenomena on 2 simple toy-models. |