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

Montag, 11. Mai 2026 14:00 Uhr Finite current supersolids in dipolar BECs

Rene Röhrs, University of Otago, New Zealand & University of Innsbruck, Austria Finite current supersolids in dipolar BECs R. Röhrs* 1 A. P. C. Underwood2 R. N. Bisset2 P. B. Blakie1 1. University of Otago, New Zealand 2. University of Innsbruck, Austria We theoretically investigate supersolids in a cylindrical tube under finite supercurrent and show that both the contrast of the density modulation and superfluid fraction depend sensitively on the imposed flow. By imposing a phase twist on the condensate wave function, we demonstrate the existence of stationary supersolid states carrying finite current. Furthermore, we find that a superfluid near the roton instability can be driven into the supersolid phase via phase twisting, providing an alternative route to supersolidity that does not rely on modifying interparticle interactions, as is commonly done in experiments. At sufficiently large currents, Landau and dynamical instabilities emerge, beyond which stationary solutions cease to exist and the system evolves into time-dependent states. For strong phase twists, phase slips can occur, leading to current reversal. * Corresponding author: rohre415@student.otago.ac.nz

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