1. A. Woszczyna, W. Czaja, K. Głód, Z. A. Golda, R. A. Kycia, A. Odrzywołek, P. Plaszczyk, L. M. Sokołowski, S. J. Szybka ccgrg: The symbolic tensor analysis package with tools for general relativity Wolfram Library Archive, vol. 8848 (2014). [abstract] [journal] 
Abstract: Riemann and Weyl curvature, covariant derivative, Lie derivative, the first and the second fundamental form on hypersurfaces, as well as basic notions of relativistic hydrodynamics (expansion, vorticity, shear) are predefined functions of the package. New tensors are easy to define. Instructions, basic examples, and some more advanced examples are attached to the package. Characteristic feature of the ccgrg package is the specific coupling between the functional programming and the ParkerChristensen index convention. This causes that no particular tools to rising/lowering tensor indices neither to the tensor contractions are needed. Tensor formulas are written in the form close to that of classical textbooks in GRG, with the only difference that the summation symbol appears explicitly. Tensors are functions, not matrixes, and their components are evaluated lazily. This means that only these components which are indispensable to realize the final task are computed. The memoization technique prevents repetitive evaluation of the same quantities. This saves both, time and memory. 
2. Wojciech Czaja, Zdzislaw A. Golda, Andrzej Woszczyna Consistent initial data for CMD perturbations (2011). [abstract] [preprint] 
Abstract: We investigate the initial condition which are simultaneously consistent with perturbation equations in both the radiationdominated and the materdominated epochs. The exact formula for the spectrum transferfunction is derived. 
3. Wojciech Czaja, Zdzislaw A. Golda, Andrzej Woszczyna Momentum of cosmological acoustic field (2011). [abstract] [preprint] 
Abstract: The acoustic spacetime corresponding to perturbed FriedmanLemaitreRobertsonWalker 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 KleinGordon scalar product. Consequently, the Fourier decomposition of the perturbation field provide the timeindependent Fourier coefficients and the timeindependent 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 sixparameter isometry group define the components of the momentum, hyperbolic momentum and angular momentum of sound. 
4. Wojciech Czaja, Zdzislaw A. Golda, Andrzej Woszczyna The acoustic wave equation in the expanding universe. SachsWolfe theorem The Mathematica Journal, vol. 13 (2011). [abstract] [journal] [cdf] 
Abstract: This article considers the acoustic field propagating in the radiationdominated universe of arbitrary space curvature. The field equations are reduced to the d’Alembert equation in an auxiliary static RobertsonWalker spacetime and dispersion relations are discussed.
*supported by the grant from The John Templeton Foundation 
5. Marek Demianski, Zdzislaw A. Golda, Andrzej Woszczyna Evolution of density perturbations in a realistic universe Gen. Rel. Grav., vol. 37, pp. 20632082 (2005). [abstract] [preprint] [journal] 
Abstract: Prompted by the recent more precise determination of the basic cosmological parameters and growing evidence that the matterenergy content of the universe is now dominated by dark energy and dark matter we present the general solution of the equation that describes the evolution of density perturbations in the linear approximation. It turns out that as in the standard CDM model the density perturbations grow very slowly during the radiation dominated epoch and their amplitude increases by a factor of about 4000 in the matter and later dark energy dominated epoch of expansion of the universe.

6. Zdzisław A. Golda Density Perturbations in Open Models of Early Universe with Positive Cosmological Constant Acta Phys. Pol. , vol. B36, pp. 21492164 (2005). [abstract] [journal] 
Abstract: The analytical solutions of the density perturbation equation in the FriedmanLema\^{\i}treRobertsonWalker (FLRW) open cosmological models with radiation and positive cosmological constant are provided. The perturbations are of two types: the first propagating as acoustical waves, and the second of nonwave nature. It is shown that there occurs dispersion on curvature and cosmological constant for acoustical perturbations. The wave solutions have anomalous dispersion. 