Ústavu teoretické fyziky

- 25. února 2014
- (Re)constructing spherically symmetric metrics in general relativity
*Sante Carloni*- ÚTF
I present a general method to reconstruct spherically symmetric metrics in GR. The method is based on definition of some special scalar variables in the framework of the 1+1+2 covariant approach proposed by Ehlers and Ellis. It provides a new way to explore the properties of spherically symmetric metrics in GR. After explaining the scheme I will give some examples and show that the new technique is also applicable to modified gravity.

- 4. března 2014
- On the existence and properties of helically symmetric systems
*Martin Scholtz*- ÚTF
We review our earlier work on the existence of periodic solutions of Einstein's equations and relate it to more recent results concerning the existence of spacetimes with helical symmetry in linearized gravity and electrodynamics. In addition we present a new calculation of Bondi mass for spacetimes with electromagnetic and scalar field sources.

- 11. března 2014
- Algebraic structure of Kundt geometries in any dimension
*Robert Švarc*- ÚTF
- 18. března 2014
- Spectral states of active galactic nuclei from simultaneous X-ray and UV measurements by XMM-Newton
*Dr. Jiří Svoboda*- Prague Relativistic Astrophysics Group, Astronomical Institute of the Czech Academy of Sciences
It is generally believed that the black holes in active galactic nuclei (AGNs) and X-ray binaries (XRBs) work in a similar way. While XRBs evolve rapidly and several sources have undergone a few complete cycles from quiescence to an outburst and back, AGNs remain in the same state due to their larger characteristic time-scale, proportional to their size. However, the study of AGN spectral states is still possible with a large sample of sources. Multiwavelength observations are needed for this purpose since the AGN thermal disc-emission dominates in the ultraviolet energy range while the up-scattered hot-corona emission is detected in X-rays. Based on ROSAT All-Sky Survey and SDSS database, Koerding et al. (2006) constructed the disc-fraction/luminosity diagrams of AGNs that revealed the analogy with the state diagrams of XRBs. I would like to present our results that are based on the comparison of strictly simultaneous UV and X-ray measurements of AGNs obtained with the XMM-Newton satellite.

- 25. března 2014
- On non-linear electrodynamics: Einstein, Hoffmann, Born, Infeld, ...
*Dr. Tayebeh Tahamtan*- Department of Physics, Eastern Mediterranean University, North Cyprus
- (seminář v angličtině)
- 1. dubna 2014
- Geometric methods of constructing generic off-diagonal exact solutions in gravity
*Prof. Sergiu Vacaru*- Alexandru Ioan Cuza University, Iasi, Romania
- (seminář v angličtině)
- 8. dubna 2014
- The complex morphology of active galactic nuclei: where do we stand?
*Dr. Frédéric Marin*- Prague Relativistic Astrophysics Group, Astronomical Institute of the Czech Academy of Sciences
- (seminář v angličtině)
The topic of active galactic nuclei (AGN) is wide, complex and multi-disciplinary. From their inner core where general and special relativity rule the accretion and emission mechanisms, to their external boundaries where classical physics and dusty mixtures prevail, explaining the intrinsic composition and morphology of AGN remains a major challenge due to the variety of their spectroscopic, timing and polarimetric signatures. Describing AGN using a unique picture is a rather challenging task, but a unified model has slowly emerged. A so far very successful theory predicts that most of the differences can be explained by an orientation effect: AGN properties differ if the system is seen from a polar, an intermediate or an equatorial inclination, the difference being attributed to circumnuclear obscuration. But does this geometrical arrangement solve everything ? In this seminar, I will review the current status of the unified model of AGN and explore, throughout spectroscopy and polarization, the successes and failures of all the existing models.

- 29. dubna 2014
- PP-waves as non-Abelian duals of flat metric
*prof. Ladislav Hlavatý*- Katedra fyziky, FJFI ČVUT
- (seminář v angličtině)
- 6. května 2014
- Kinematical Hilbert space for Einstein-Cartan theory: Continuous tensor product and integral representation of fundamental variables
*dr. Marián Pilc*- UniCredit Bank
- (seminář v angličtině)
- 13. května 2014
- Scalar perturbations in f(R)-cosmology
*Mgr. Jan Novák*- Matematický ústav AV ČR
- (seminář v angličtině)
- 20. května 2014
- Effects of primordial curvature perturbations on the value of the cosmological constant
*Prof. Antonio Enea Romano*- Group of Phenomenology of Fundamental Interactions, University of Antioquia, Medellín / Yukawa Institute for Theoretical Physics, Kyoto University
- (seminář v angličtině)
- 27. května 2014
- Extended teleparallel gravities: general properties
*Dr. Diego Saez Gomez*- Department of Theoretical Physics and History of Science, Faculty of Science and Technology, University of Basque Country, Bilbao
- (seminář v angličtině)
Teleparallel gravity is a gauge theory for the translation group defined in the tangent bundle of a Riemannian spacetime, where the so-called tetrad plays the role of the dynamical field of the theory and is parallely transported (absolute parallelism condition) by assuming the Weitzenböck connection instead of the Levi-Civita connection, leading to a non-null torsion but a null scalar curvature. Whereas teleparallel gravity is equivalent to general relativity, its extensions, also known as f(T) gravities in analogy to f(R) gravity, give rise to new features and interesting properties but are not equivalent to f(R) gravity. In this talk, I will review some of the last analysis about f(T) gravity, including the violation of the local Lorentz invariance, the construction of conformal invariant actions or the non-existence of extra gravitational wave modes, among other issues.

- 27. června 2014
- !!! MIMOŘÁDNĚ V PÁTEK V 10:00 !!!
- Induced fermionic current in toroidally compactified spacetimes with applications to cylindrical and toroidal nanotubes
*Prof. Stefano Bellucci*- Laboratori Nazionali di Frascati, INFN Roma
- (seminář v angličtině)
- 12. srpna 2014
- Testing modified gravity in the solar system
*dr. Ali Mozaffari*- Department of Physics, Imperial College London
- (seminář v angličtině)
- 19. srpna 2014
- Hawking radiation as perceived by different observers
*dr. Luis Barbado*- Institute of Astrophysics of Andalusia (CSIC), Granada
- (seminář v angličtině)
In this talk, I will introduce a method for studying the perception of Hawking radiation by different observers outside a black hole, and for different vacuum states of the radiation field. The analysis is performed in terms of an effective-temperature function that varies along the trajectory of each observer. With this tool, I will show that not all observers crossing the horizon of a black hole in free-fall will fail to detect radiation, and that indeed it is not necessary to strictly form an horizon for obtaining Hawking radiation. Also, the radiation temperature perceived by a generic observer following an arbitrary radial trajectory outside the black hole (when it is possible to talk about a temperature) can be calculated directly from the local characteristics of its trajectory, in a way which has a clear physical interpretation. Finally, our results also point to a self-consistent buoyancy scenario near black holes, due to Hawking radiation.

- 25. srpna 2014
- !!! MIMOŘÁDNĚ V PONDĚLÍ od 10:00 !!!
- The (un)bearable lightness of matter-gravity couplings
*dr. Vincenzo Vitagliano*- CENTRA, Instituto Superior Tecnico, Lisboa
- (seminář v angličtině)
I will give a pedagogical review of Metric-Affine theories of Gravity (MAG), theories for which the metric and the affine connection are independent quantities (namely in the Palatini approach) and whose actions include covariant derivatives of the matter fields, with the covariant derivative naturally defined using the independent connection. MAG straightforwardly admit the presence of direct couplings involving matter and connection. I will summarize some physical consequences of such theories.

- 26. srpna 2014
- Gravitational waves and self-force computation for a compact object around a super-massive black hole
*dr. Patxi Ritter*- Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, CNRS, Orléans
- (seminář v angličtině)
The description of extreme-mass-ratio binary systems is a challenging problem in gravitational wave physics with significant relevance for the future space interferometer eLISA/NGO. The main difficulty lies in the evaluation of the effects of the small body's gravitational field on itself. To that end, an accurate computation of the perturbations produced by the small body with respect to the background geometry of the large object (a massive black-hole) is required. After a presentation of the theoretical perturbative framework for EMRIs, I will present a numerical procedure to generate EMRI wave-forms and compute the self-force in the Regge-Wheeler gauge.

- 9. září 2014
- Black hole chemistry
*dr. David Kubizňák*- Perimeter Institute for Theoretical Physics, Waterloo, Ontario
The mass of a black hole has traditionally been identified with its energy. We describe a new perspective on black hole thermodynamics, one that identifies the mass of a black hole with chemical enthalpy, and the cosmological constant as thermodynamic pressure. This leads to an understanding of black holes from the viewpoint of chemistry, in terms of concepts such as Van der Waals fluids, reentrant phase transitions, triple points, and isolated critical point. Both charged and rotating black holes exhibit novel chemical-type phase behaviour, hitherto unseen.

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© 15. prosince 2014; Oldřich Semerák

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