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
Scalar-tensor theories with derivative interactions form backgrounds which spontaneously break Lorentz invariance (e.g. cosmology during inflation or the dark energy era). The dynamics of small scalar fluctuations on general anisotropic backgrounds -- phonons -- can be described as geodesic motion in an effective "acoustic" space time, with the acoustic metric providing the relativistic description of general media. This acoustic metric and its inverse give the dispersion relation, rays and phase velocities and construct two dual sound cones.
I will discuss how to read off true instabilities -- ghosts and gradient instabilities -- from the invariant properties of the acoustic metric, but also discuss false instabilities that may appear for some observers, relating this to Cherenkov radiation and the ill-posedness of the Cauchy problem. I will show that the geometric discussion of the sound cones is equivalent to the usual Hamiltonian description for an energy related to an conserved acoustic energy-momentum tensor for the fluctuations, distinct from the usual space-time one.
As full quantum gravity still remains elusive, we can gain at least limited insight into the quantum features of black holes through apt approximations, semi-classical gravity being one of them. While finding solutions even to this simplified theory is still difficult task to do, thanks to the techniques of AdS/CFT correspondence and holography, quantum-corrected black holes in all orders of backreaction with both rotation and Maxwell electromagnetic charges have been discovered. In my talk, I would like to show you how we can apply this computational framework to gravity coupled to non-linear electrodynamics and present you with resulting novel charged quantum-corrected black holes and their thermodynamics.
In this talk, I will present new rotating black hole solutions of the low-energy effective action of string theory in three and four dimensions. These geometries are asymptotically flat with a linear dilaton vacuum and exhibit unusual thermodynamic properties, including a mass-independent Hawking temperature. I will also discuss charged extensions, which lead to closed time-like curves inside the inner horizon. Finally, I will show that these solutions arise from the large-d limit of singly rotating Myers–Perry black holes.
TBA
A series of works by Belinskii, Khalatnikov and Lifshitz (BKL) conjectured that spacetime near a generic spacelike singularity locally behaves in a chaotic way. Since BKL conjecture concerns very strong gravity regimes, it is natural to ask how quantum gravity influences it. We tackle this question by looking at perturbative quantum corrections to Bianchi I and II metrics approximating the relevant features of BKL conjecture. We argue that even such perturbative effects can completely change the nature of BKL dynamics. While we work in the framework of thermodynamic gravity, our findings also apply to the effective dynamics of loop quantum cosmology.
I will describe a new construction of Ricci flat metrics using gauged linear sigma models satisfying the Calabi-Yau condition. The approach will be introductory using elementary examples to illustrate the main points and to underline the connection between physical and mathematical concepts.
David Kubizňák Oldřich Semerák