Relativistický seminář
Ústavu teoretické fyziky

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

29. května 2018
Horizonty kolem prstencových zdrojů
Bc. Milan Pešta
5. června 2018
Physics of gravitational waves in the presence of positive cosmological constant
Sk Jahanur Hoque, PhD
The Institute of Mathematical Sciences, Taramani, Chennai, India
(seminář v angličtině)

Cosmological observations have established that our universe has positive cosmological constant. A positive cosmological constant profoundly alters the asymptotic structure of space-time. In this talk, we discuss the linearized gravitational field produced by compact sources in the background with positive cosmological constant -- de Sitter space. Using the covariant phase space formalism, we obtain the quadrupole formula in such a setting. We also show that the energy flux of gravitational waves measured at future null infinity is the same as that measured across the cosmological horizon of the compact source. To get an order of estimate we also discuss power radiated by a binary system in de Sitter background.

12. června 2018
Linear local gauge-invariant observables on spacetimes of sub-maximal symmetry
Igor Khavkine, PhD
Institute of Mathematics, Czech Academy of Sciences
(seminář v angličtině)

The Killing operator $K_{ab}[v]=\nabla_a v_b + \nabla_b v_a$ is the generator of gauge symmetries (linearized diffeomorphisms) $h_{ab}\mapsto h_{ab} + K_{ab}[v]$ in linearized gravity. A linear local gauge-invariant observable is a differential operator $I[h]$ such that $I[K[v]] = 0$ for any gauge parameter field $v_a$. A set $\{I_i[h]\}$ of such observables is complete if the simultaneous conditions $I_i[h] = 0$ are sufficient to conclude that the argument is a pure gauge mode, $h_{ab} = K_{ab}[v]$. The explicit knowledge of a complete set of local gauge invariant observables has multiple applications from the points of view of both physics and geometry, whenever a precise separation of physical and gauge degrees of freedom is required. Surprisingly, until very recently, such complete sets have been known explicitly only on spacetimes of maximal symmetry (Minkowski or (anti-)de Sitter). I will discuss recent progress that has allowed an explicit construction of complete sets of local gauge invariant observables on backgrounds of sub-maximal symmetry, most notably on cosmological (FLRW) and black hole (Schwarzschild and Kerr) spacetimes.

Jiří Bičák                                                                                                  Oldřich Semerák