Seminář se koná každé úterý v 10:40 v posluchárně ÚTF MFF UK
v 10. patře katedrové budovy v Tróji, V Holešovičkách 2, Praha 8
In the first part we discuss earlier work by Exner and Lipovský, in which they consider quantum graphs consisting of a compact part and semi-infinite leads. Such a system may contain embedded eigenvalues in the continuous spectrum, which, under perturbation, move into the second sheet of the complex energy surface and produce resonances. We also show how the scattering and resolvent resonances in quantum graphs coincide and how ”nothing is lost at the perturbation” in the sense of the number of poles. In the second part we then introduce a cut-off technique known since the eighties to our quantum graph framework. Using it, one can identify resonances through the eigenvalue behavior of the system ”closed in a box”. We prove its validity, which was before done only in the case of one-dimensional potential scattering, and illustrate it with examples.
Feynman diagrams are a terrible way to calculate scattering amplitudes. They are woefully inefficient, and manifestly introduce an infinite amount of redundancy which obscures any structure which the scattering amplitudes have. In this talk I will highlight certain modern approaches to scattering amplitudes. In particular, there are geometric ideas, such as the Amplituhedron, which directly capture scattering amplitudes without any auxiliary constructions such as Lagrangians, virtual particles, or even spacetime itself. This gives a radically new way to think about the physics of scattering in QFT.
(seminář v češtině)
Přednáška představí inženýrský proces transformace ideového návrhu technického experimentu do jeho fyzické realizace. Budou zmíněny obvyklé tolerance výrobních metod a jejich faktické limity. Budou naznačeny postupy, zaručující minimalizaci nebo statickou a dynamickou kompenzaci vybraných veličin. Závěrem bude prezentován postup konstrukce a realizace konkrétního měřicího zařízení od formulace požadavků na jeho funkci až po jeho fyzickou realizaci.
I will introduce and discuss various entropies in quantum theory and their meaning. I will specifically focus on the classical thermodynamic entropy and then generalize this notion to quantum physics to arrive at the notion called observational entropy.
Jiří Horáček David Heyrovský