Seminář Ústavu teoretické fyziky

4. listopadu 2025

Precision Calculations of Atomic Spectra and Tests of Fundamental Physics

doc. Mgr. Vojtěch Patkóš, Ph.D.

Department of Chemical Physics and Optics, MFF Charles University

(seminář v angličtině)

Comparison of theoretical predictions for atomic energy levels with experimental data on transition frequencies serves as an important low-energy test of the Standard Model of fundamental interactions. In light atomic systems, such as electronic hydrogen, muonic hydrogen, or the helium atom, the precision of theoretical calculations can reach the level of 10^-12 and becomes sensitive to subtle effects, such as the internal structure of the nucleus. This enables us not only to perform stringent tests of Quantum electrodynamics but also to extract values of fundamental constants, such as the Rydberg constant and the proton charge radius. In my talk, I will discuss the current status of calculations in atomic physics and their comparison with the most accurate experimental data.

11. listopadu 2025

Resonances in Quantum Graphs

Mgr. Jan Pekař

Nuclear Physics Institute, Czech Academy of Sciences

(seminář v angličtině)

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.

18. listopadu 2025

Scattering Amplitudes from Geometry

Jonah Stalknecht, Ph.D.

Institute of Particle and Nuclear Physics, MFF Charles University

(seminář v angličtině)

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.

Jiří Horáček                                                                                                  David Heyrovský