The terminal bubble wall velocity in a first-order phase transition (FOPT) is a critical parameter that influences not only the gravitational wave power spectrum but also a wide range of FOPT-related phenomena, including baryogenesis and dark matter production. However, precise computation of this velocity remains challenging. In this talk, I will discuss how to establish bounds on bubble wall velocities using two straightforward approximations: the local thermal equilibrium (LTE) approximation and the ballistic approximation. We perform numerical calculations both for a model-independent analysis and within an example model, the singlet-extended Standard Model.

The striking imbalance of matter and antimatter in our universe inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision. The BASE collaboration at the antiproton decelerator of CERN is performing such high-precision comparisons with protons and antiprotons. Using advanced cryogenic Penning traps, we have performed the most precise comparison of the proton-to-antiproton charge-to-mass ratio with a fractional uncertainty of 16 parts in a trillion [1], and have invented a novel spectroscopy technique, that allowed for the first direct high-precision measurement of the antiproton magnetic moment with a fractional accuracy of 1.5 parts in a billion [2]. Together with our last measurement of the proton magnetic moment [3] this improves the precision of previous magnetic moment based tests of the fundamental CPT invariance by more than a factor of 3000. A time series analysis of the sampled magnetic moment resonance furthermore enabled us to set first direct constraints on the interaction of antiprotons with axion-like particles (ALPs) [4], and most recently, we have used our ultra-sensitive single particle detection systems to derive constraints on the conversion of ALPs into photons [5]. In parallel we are working on the implementation of new measurement technology to sympathetically cool antiprotons [6] and to apply quantum logic inspired spectroscopy techniques [7]. In addition to that, we are currently developing the transportable antiproton-trap BASE-STEP, partly developed at Mainz, to relocate antiproton spectroscopy experiments from CERN’s accelerator environment to dedicated precision laboratory space at Heinrich Heine University Düsseldorf, very recently, the first loaded transport of this trap has been demonstrated successfully I will give a general introduction to the topic, will review the recent results produced by BASE, with particular focus on recent developments towards an at least 10-fold improved coherent measurement of the antiproton magnetic moment, and towards the first antiproton transport. [1] M. J. Borchert et al., Nature 601, 35 (2022). [2] C. Smorra et al., Nature 550, 371 (2017). [3] G. Schneider et al., Science 358, 1081 (2017). [4] C. Smorra et al., Nature 575, 310 (2019). [5] J. A. Devlin et al., Phys. Rev. Lett. 126, 041321 (2021). [6] M. A. Bohman et al. Nature 596, 514 (2021) [7] J. M Conrejo et al., New J. Phys. 23 073045

Precision measurements of atomic transition frequencies have become a promising path for testing theories for new physics beyond the standard model. To achieve even higher precision more stable and narrow-linewidth laser sources are required. Superradiant lasers are a candidate for realising a narrow-linewidth, high-bandwidth active frequency reference. They shift the phase memory from the optical cavity, which is subject to technical and thermal vibration noise, to an ultra-narrow optical atomic transition of an ensemble of cold atoms trapped inside the cavity. Our previous demonstration of pulsed superradiance on the mHz transition in 87Sr achieved a fractional Allan deviation of 6.7*10−16 at 1s of averaging. Moving towards continuous-wave superradiance promises to further improve the short-term frequency stability by orders of magnitude. A key challenge is the continuous supply of cold atoms into a cavity, while staying in the collective strong coupling regime. We demonstrate continuous loading and transport of cold 88Sr atoms inside a ring cavity, after several stages of laser cooling and slowing. We further describe the emergence of distinct zones of collective continuous lasing of the atoms on the 7.5kHz transition, 7x narrower than the cavity linewidth, and pumped by the cooling lasers via inversion of the motional states. The lasing is supported by self-regulation of the number of atoms inside the cavity that pins the dressed cavity frequency to a fixed value over >3MHz of raw applied cavity frequency. In the process up to 80% of the original atoms are expelled from the cavity. I will also present a new project in Heidelberg aiming to use precision spectroscopy of highly charged ions to search for a variation of the fine-structure constant.

Compressible computational fluid dynamics (CFD) is an active and fruitful area of research. In this talk, we will focus on time integration methods optimized for CFD applications. We will briefly review the classical Courant-Friedrichs-Lewy (CFL) constraint and present error-based time step size control as an alternative. In particular, we will discuss how the design of the methods influences their efficiency and robustness. Combining theoretical analysis with a data-driven approach, we will present new optimized time integration methods for compressible CFD applications that are available in open-source software.