Wochenübersicht – nächste Woche

Cosmological first-order phase transitions are said to be strongly supercooled when the nucleation temperature is much smaller than the critical temperature. The phase transition takes place slowly and the probability distribution of bubble nucleation times is maximally spread. Hubble patches which get percolated later than the average are hotter than the background after reheating and potentially collapse into primordial black holes (PBHs). I will give a review of this PBHs formation mechanism and of its most recent developments.

Using the high-intensity radiation of the European X-ray Free-Electron Laser, we recently succeeded to excite the sharpest atomic transition in the hard X-ray range, the 12.4 keV nuclear resonance of the stable isotope Scandium-45 [1]. With its extremely narrow natural linewidth of 1.4 femto-eV, it opens not only new possibilities for the development of a nuclear clock, but also for research linked to the foundations of physics, such as time variations of the fundamental constants, the search for dark matter as well as probing the foundations of relativity theory. Furthermore, our experiment demonstrates the great potential of self-seeding X-ray lasers with high pulse rates as a promising platform for the spectroscopy of extremely narrow-band nuclear resonances. The next steps towards a nuclear clock based on Scandium-45 require a further increase of the spectral photon flux using improved X-ray laser sources at 12.4 keV and the development of frequency combs reaching up to this energy. [1] Yuri Shvyd’ko et al., Nature 622, 471 (2023)