Wochenübersicht

Numerical calculations of cosmic structure formation have become a powerful tool in astrophysics. Starting right after the Big Bang, they are not only able to accurately predict the dark matter backbone of the cosmic web far into the non-linear regime, but are also capable of following baryonic physics with rapidly improving fidelity. In my talk, I will review the methodology and selected results of recent structure formation simulations that follow large parts of the observable universe. I will discuss some of the primary challenges in modelling strong, scale-dependent feedback processes that regulate star formation in galaxies, and highlight the important role played by supermassive black holes in galaxy formation. I will also discuss extremely large simulations and describe how they help to make reliable predictions for the impact of baryons and massive neutrinos on cosmological observables, effects that need to be understood to make full use of upcoming new survey data. The simulation results also shed light on cosmic reionization and magnetic field amplification during non-linear structure formation. Finally, I will highlight some of the methodological and technical challenges involved in obtaining future multi-physics, multi-scale simulations that aim for more accurate predictions.

The existence of primordial black holes can be probed through the gravitational waves generated during their formation and subsequent evolution. In this talk, we will explore different frequency ranges and the corresponding experiments designed to test their existence. We will cover the spectrum from ultra-low-frequency gravitational waves—targeted by future missions such as LiteBIRD—to current experiments using pulsar timing arrays and the LIGO-Virgo-KAGRA network, as well as upcoming efforts in the ultra-high-frequency domain.

The early universe likely underwent a series of phase transitions as it expanded and cooled from an initially hot, dense state. Among these, first-order phase transitions --proceeding through the nucleation and expansion of bubbles-- are particularly interesting due to their potential cosmological implications, which include gravitational wave production and the possibility to generate the baryon asymmetry through the mechanism of electroweak baryogenesis. In this talk I will review the theoretical framework used to study such transitions and discuss recent progress on understanding bubble velocities and CP-violating effects relevant for electroweak baryogenesis.
Slides here...

Diamond quantum sensors for magnetic fields have transformed several areas of science, most prominently magnetic resonance and magnetic field imaging at the micro- and nanoscale. However, these breakthroughs have largely remained limited to specialized laboratories. I will present two lines of research of our laboratory to change this state of affairs and significantly simplify the use of diamond quantum sensors. One direction concerns scanning probe imaging, where we have developed a simplified approach to scanning probe positioning. While conventional setups image magnetic fields by scanning a nanofabricated diamond tip hosting a single NV center across a sample, we developed a setup where we can scan an extended (10 µm to mm) bulk diamond in 10 nm-scale proximity of a sample, using interferometric alignment to maintain the sensor perfectly parallel to the sample. Beyond a technical simplification, this approach opens the door to massively parallel scanning probe microscopy using multiple NV centers, as well as to novel plasmonic near-field microscopes. Another direction concerns the electric readout of large ensembles of NV center spins, as they might find application in large-scale commercial devices like gyroscopes or magnetic field sensors. Here, we have shown in recent research that readout in a microwave cavity is remarkably competitive with more established optical readout for large ensembles, and provides a straightforward all-electric way to integrate diamond spin sensors into microfabricated circuits.