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
We present several classes of static, spherically symmetric vacuum solutions to quadratic gravity. Notably, besides the Schwarzschild black hole, these solutions also contain a static, spherically symmetric black hole with non-trivial Ricci tensor.
The standard cosmological model has been constrained with unprecedented accuracy. Nevertheless, we are facing off new challenges. The lack of detection of Dark Matter and Dark Energy have opened to new paths. On one side, we are entering the "no-WIMP" era. On the other side, explaining the accelerated expansion of the Universe may require an extension of General Relativity. I will review the state of art of the standard cosmology while introducing new tests of both Dark Matter and Modified Gravity. I will introduce a relatively new paradigm for Dark Matter, named Ultra-light axions, and explain how to probe it with the current and forthcoming dataset. Then, I will also show some tests of the standard cosmological model and of modified gravity that near in future may be helpful to constrain/rule out models.
I consider light propagation in a plasma on a general relativistic spacetime. In the first part of my talk I review a Hamiltonian formalism for light rays in a pressure-less non-magnetised plasma and I present, on the basis of this formalism, the resulting equations for the deformation of light bundles (Sachs equations). In the second part I discuss the shadows of black holes in the presence of a plasma. The latter is of relevance in view of the forthcoming observations by the Event Horizon Telescope.
An existing canonical formulation of dynamics for a discrete system will be briefly reviewed and used to define a version of quantum field theory on a fixed simplicial lattice. Such a model may serve as an intermediate step for incorporating matter or gauge fields into lattice-based quantum gravity theories. For start, we shall consider Euclidean lattice and real scalar field. We will discuss the relation to the algebraic approach used in quantum field theory in curved spacetime and to path integral.
The fate of Cauchy horizons, such as those found inside charged black holes, is intrinsically connected to the decay of small perturbations exterior to the event horizon. As such, the validity of the Strong Cosmic Censorship conjecture is tied to how effectively the exterior damps fluctuations. By studying scalar and fermionic fields in the exterior of Reissner-Nordstrom-de Sitter black holes we identify three families of modes: one directly linked to the photon sphere, another family whose existence and timescale is closely related to the de Sitter horizon and, finally, a third family which dominates for near-extremally-charged black holes. We give a detailed description of scalar and fermionic perturbations of such black holes, and conjecture that Strong Cosmic Censorship is violated in the near extremal regime.
I will review the recent idea that, within the formalism of Cartan geometry, a spontaneously-broken gauge theory of the Lorentz group contains Ashtekar's chiral formulation of general relativity accompanied by dust, which could play the role of dark matter. The model is "pre-geometric" in the sense that the spacetime metric may be constructed only in the symmetry-broken regime; however, in principle the two phases can be smoothly connected, and spacetime be realised dynamically as a symmetry-breaking process.
Jiří Bičák Oldřich Semerák