Fakultät für Physik und Astronomie

Physikalisches Kolloquium

Freitag, 15. Mai 2026 17:00 Uhr The Condensing Universe

Prof. Michael Ramsey-Musolf, Department of Physics, University of Massachusetts, Amherst The Condensing Universe Prof. Michael Ramsey-Musolf Department of Physics, University of Massachusetts, Amherst While the phenomenon of cosmic expansion is well-established, it is also possible that this expansion could engender a process of cosmic condensation. Indeed, in the presence of new physics beyond the Standard Model, the early universe could have undergone a change of state in a manner analogous to the condensation of water vapor into liquid. Such a first order phase transition, associated with the breaking of one or more symmetries, could hold the keys to explaining the cosmic matter-antimatter asymmetry, abundance of dark matter, and/or non-vanishing neutrino masses. I discuss recent theoretical progress in analyzing the possibilities for this condensing universe and their possible signatures in terrestrial and astrophysical experiments.

Teilchenkolloquium

ZZy Results

Anke Ackermann, Kirchhoff-Institut-für Physik Measurement of ZZγ production with the ATLAS detector Anke Ackermann1 1 Kirchhoff-Institute for Physics, Heidelberg University Abstract The Standard Model of particle physics predicts the rare production of triboson final states, offering a unique probe of gauge boson selfinteractions and sensitivity to anomalous quartic gauge couplings. We present the measurement of ZZγ production, utilizing the large dataset collected by the ATLAS detector during Run 2. The analysis focuses on the fully leptonic final state, pp → ZZγ → ℓ+ ℓ− ℓ′+ ℓ′− γ with ℓ, ℓ′ = e or µ. Evidence for the ZZγ production has been observed with eight candidate events and an expected background of less than one event. The measured cross-section of σZZγ = 0.144 ± 0.058 (stat.) ± 0.006 (syst.) fb is consistent with Standard Model predictions. To achieve this result, we develop a novel method to estimate the dominant background from non-prompt photons produced within jets, using a jet ratio technique to extrapolate from a high-statistics control region. This talk will summarize the analysis strategy, background estimation, and cross-section measurement, highlighting the potential for future analysis to probe new physics in the electroweak sector. 1

Astronomisches Kolloquium

Dienstag, 12. Mai 2026 16:30 Uhr Ultraviolet spectroscopy of metal-poor stars: new advances and new opportunities

Ian Roederer, North Carolina State University Understanding the origin of the elements is one of the major challenges of modern astrophysics. Ultraviolet (UV) spectroscopy of metal-poor stars provides access to many absorption lines of elements and species that are otherwise undetectable in optical or infrared spectra. I will show how UV spectra collected with the Hubble Space Telescope have expanded stellar chemical inventories to more than 65 elements per star and identified signatures associated with r-process transuranic fission fragments. I will also show how UV spectroscopy with the ANDES instrument on the Extremely Large Telescope and the proposed Habitable Worlds Observatory mission could revolutionize our understanding of the first stars in the decades ahead. To arrange a visit with the speaker during the visit, please contact their host: Norbert Christlieb

Zentrum für Quantendynamik Kolloquium

Mittwoch, 20. Mai 2026 16:30 Uhr Ultracold lithium-chromium mixtures: From mass-asymmetric fermionic matter to paramagnetic molecules

Dr. Matteo Zaccanti, INO-CNR & LENS, Physics Department, University of Florence Ultracold lithium-chromium mixtures: From mass-asymmetric fermionic matter to paramagnetic molecules Dr. Matteo Zaccanti Physics Department, University of Florence Quantum mixtures of different atomic species represent compelling frameworks for a variety of fundamental studies and quantum-technological applications, ranging from the exploration of exotic few- and many-body phenomena to the realization of novel molecular species in the ultracold regime. Here, I will first provide a general overview of the activities of our lab, primarily based on a novel Fermi-Fermi mixture of 6Li alkali and 53Cr transition-metal atoms, and currently focusing onto two main research topics: realization of quantum gases of LiCr molecules, and investigation of strongly interacting fermionic matter in presence of a large mass asymmetry. I will then discuss in more detail a recent study of transport dynamics of a small sample of ultracold lithium atoms – acting as light impurity particles – released into a large, ideal gas of chromium – that plays the role of a bath of heavy, point-like scatterers. Under strong interspecies interactions, by lowering the temperature we unveil a crossover from normal diffusion to subdiffusion. Simultaneously, a localized fraction emerges in the lithium gas, displaying no discernible dynamics over hundreds of collision events. Our findings, incompatible with a conventional Fermi-liquid picture, are instead captured by a model of a matter wave propagating through a (quasi-)static disordered landscape of point-like scatterers. These results point to a key, enhanced role of quantum interference in heavylight atomic mixtures, which emerge as versatile platforms for exploring disorder-free localization phenomena solely driven by a large mass difference.

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