Seminář se koná v úterý ve 13:10 v posluchárně ÚTF MFF UK
v 10. patře katedrové budovy v Tróji, V Holešovičkách 2, Praha 8
After briefly discussing the non-impulsive (smooth) case, we will show that every impulsive wave-type spacetime of the form $M=N\times R^2_1$, with line element $ds^2 = dh^2 + 2 du dv + f(x)\delta(u) du^2$ is geodesically complete. Here $(N,h)$ is an arbitrary connected, complete Riemannian manifold, $f$ is a smooth function and $\delta$ denotes the Dirac distribution on the hypersurface $u=0$. Moreover the geodesics behave as is physically expected.
One of the most outstanding problem in cosmology today is to explain the late time acceleration of the Universe. It is now confirmed beyond any doubt that our Universe is dominated by some unknown dark component which causes the Universe to have an accelerated expansion in at present. Modeling this dark component is a challenge for both particle physicists and cosmologists. I shall describe number of possible ways one can explain this late time acceleration. I shall also discuss different observational issues related to this dark energy model building.
Po semináři bude s profesorem Shorem diskuse o jeho práci jednoho z vedoucích redaktorů časopisu Astronomy and Astrophysics.
A cosmic string modeled by an abelian Higgs vortex is studied in the rotating black hole background of the Kerr geometry. It is shown that such a system displays much richer phenomenology than its static Schwarzschild/Reissner- Nordstrom cousins. In particular it is shown that the rotation generates a small electric flux near the horizon. For an extremal rotating black hole the two phases of the Higgs hair are possible: i) small black holes expel the Higgs field and (similar to Wald's solution) there is no flux through the horizon ii) large black holes are pierced by the Higgs hair. Backreaction of the Higgs vortex on the Kerr geometry will also be briefly studied, while it will be shown that it cannot be described as a mere conical deficit as might be expected.
In this talk we discuss how polarization of photons affects their motion in a gravitational field created by a rotating massive compact object. We briefly discuss gravito-electromagnetism analogy and demonstrate that spinoptical effects in many aspects are similar to the Stern-Gerlach effect. We use (3+1)-form of the Maxwell equations to derive a master equation for the propagation of monochromatic electromagnetic waves with a given helicity. We first analyze its solutions in the high frequency approximation using the 'standard' geometrical optics approach. After that we demonstrate how this 'standard' approach can be modified in order to include the effect of the helicity of photons on their motion. Such an improved approach reproduces the standard results of the geometrical optics at short distances. However, it modifies the asymptotic behavior of the circularly polarized beams in the late-time regime. We demonstrate that the corresponding equations for the circularly polarized beam can be effectively obtained by modification of the background geometry by including a small frequency dependent factor. We discuss motion of circularly polarized rays in the Kerr geometry. Applications of this formalism to the propagation of circular polarized photons in the Kerr spacetime are discussed.
I will discuss the possibility of decoupling gravitational perturbations a la Teukolsky on higher dimensional black hole backgrounds.
Jiří Bičák Oldřich Semerák