1. Piotr T. Chruściel, Sebastian J. Szybka
On the Ernst electro-vacuum equations and ergosurfaces
Acta Phys. Pol., B , vol. 39, pp. 59-75 (2008).
[abstract] [preprint] [journal]

Abstract:
The question of smoothness at the ergosurface of the space-time metric constructed out of solutions (E,phi) of the Ernst electro-vacuum equations is considered. We prove smoothness of those ergosurfaces at which Re(E) provides the dominant contribution to f=-(Re(E)+|phi|^2) at the zero-level-set of f. Some partial results are obtained in the remaining cases: in particular we give examples of leading-order solutions with singular isolated ``ergocircles".

2. Sebastian J. Szybka, Tadeusz Chmaj
Fractal Threshold Behavior in Vacuum Gravitational Collapse
Phys. Rev. Lett., vol. 100, p. 101102 (2008).
[abstract] [preprint] [journal] [download]

Abstract:
We present the numerical evidence for fractal threshold behavior in the five dimensional vacuum Einstein equations satisfying the cohomogeneity-two triaxial Bianchi type-IX ansatz. In other words, we show that a flip of the wings of a butterfly may influence the process of the black hole formation.

3. Andrzej Woszczyna
Dispersion of density waves in the Universe with positive cosmological constant
Conference report (2008).
[abstract] [Mathematica 5.2]

Abstract:
Marie Curie Host Fellowships for the Transfer of Knowledge (TOK) Project MTKD-CT-2005-029466: PARTICLE PHYSICS AND COSMOLOGY: THE INTERFACE, Fourth Workshop 13.02 - 16.02.2008, Warszawa

4. Artur Janda
On Lie Symmetries of Certain Spherically Symmetric Systems in General Relativity
Acta Phys. Pol., B , vol. 38, pp. 3961-3969 (2007).
[abstract] [journal] [http://th-www.if.uj.edu.pl/acta/vol38/pdf/v38p3961.pdf]

Abstract:
Certain aspects of Lie-point symmetries in spherically symmetric systems of gravitational physics. Lie symmetries are helpful in solving differential equations. General concepts and a few examples are given: perfect fluid in shearfree motion, the conformal Weyl theory and a higher derivative gravity which is equivalent to General Relativity coupled to certain nonlinear spin-2 field theory.

5. Jacek Guzik, Gary Bernstein, Robert E. Smith
Systematic effects in the sound horizon scale measurements
MNRAS, vol. 375, pp. 1329-1337 (2007).
[preprint] [journal]

Abstract:

6. Leszek M. Sokołowski
Physical interpretation and viability of various metric nonlinear gravity theories applied to cosmology
(2007).
[abstract] [preprint]

Abstract:
We critically review some concepts underlying current applications of gravity theories with Lagrangians depending on the full Riemann tensor to cosmology. We argue that it is impossible to reconstruct the underlying Lagrangian from the observational data: the Robertson-Walker spacetime is so simple and "flexible" that any cosmic evolution may be fitted by infinite number of Lagrangians. Confrontation of a solution with the astronomical data is obstructed by the existence of many frames of dynamical variables and the fact that initial data for the gravitational triplet depend on which frame is minimally coupled to ordinary matter. Prior to any application it is necessary to establish physical contents and viability of a given gravity theory. A theory may be viable only if it has a stable ground state. We provide a method of checking the stability and show in eleven examples that it works effectively.