Our understanding of neutrinos has skyrocketed over the past two decades. Neutrino physics today is precision science that has the potential to teach us a lot about the origin of the observed mass and mixing patterns among elementary particles. Moreover, being electrically neutral, neutrinos are the only Standard Model fermions that can mix with new particles that are uncharged under the Standard Model gauge group. An important example for such new particles are sterile neutrinos, which in turn could be related to the Dark Matter in the Universe.

A particular interesting way of studying neutrinos is through neutrino oscillations, the periodic conversion of one neutrino flavor into another. We investigate how neutrino oscillation measurements can probe physics beyond the Standard Model, we develop advanced analysis methods (for instance based on machine learning techniques), and we study the intricate physics of neutrino–nucleus interactions – a challenging multiscale problem at the interface of particle physics and nuclear physics.

A second topic of interest to us are astrophysical neutrino sources, especially extreme environments like neutron stars or supernovae. We investigate neutrino production in such objects and we study the highly non-linear (and so far intractable) oscillations of neutrinos in extreme environments. Among the techniques we employ in this context is quantum computing, where we develop algorithms for simulating highly entangled self-interacting neutrino systems.

We closely collaborate with the CERN Neutrino Group.

The existence of Dark Matter — evidenced by a variety of astrophysical and cosmological observations — is perhaps the strongest hint for the incompleteness of the Standard Model of particle physics. The nature of dark matter, however, remains a mystery. Many dark matter candidates that were considered promising just a few years ago are now heavily constrained. On the other hand, new candidates are emerging. It is in this context that we develop new theories of dark matter, focusing on novel mechanisms for dark matter production in the early Universe (involving, for instance, the physics of cosmological phase transitions) and for its detection today.

The discovery of gravitational waves in 2015 has created a whole new field of astrophysics.  We are interested especially in the emerging field of high-frequency (>> kHz) gravitational wave astronomy.  Sources emitting in this frequency range typically require physics beyond the Standard Model: primordial black holes, superradiance, cosmological phase transitions, inflation, etc.  This makes high-frequency gravitational waves interesting probes of such exotic – but very well motivated – phenomena. Currently, we are contributing to a paradigm shift in the field by demonstrating that, in fact, even the Standard Model can provide sources of O(MHz) gravitational waves, namely in the form of neutron stars undergoing a quark-hadron phase transition. Observing such a signal, while extremely challenging, would allow us to test QCD at ultra-high density, a regime which cannot be probed in the laboratory and is practically impossible to describe theoretically.

We are also interested in techniques for high-frequency gravitational wave detection, in particular using novel quantum sensing methods. A key concept in this context is the coupling of gravitational waves to electromagnetism. For instance, gravitons (the quanta of gravitational waves) can convert into photons in a magnetic field, and photons traveling through a gravitational wave background experience a frequency shift.

At the interface of particle physics, astrophysics, and atomic/molecular/optical physics, we help develop entirely new detector concepts that may one day allow the first observation of gravitational waves above the kHz band.

We closely closely collaborate with the CERN Quantum Technology Initiative.