Joachim Kopp — Research Activities

Student: Dr. Einstein, aren't these the same questions as last year's final exam?
Dr. Einstein: Yes; But this year the answers are different.

• What is the nature of Dark Matter?
• How is the electroweak gauge symmetry broken?
• Why are there three generations of elementary particles?
• What determines the patterns among particle masses and mixing angles?
• ...

DARK MATTER SEARCHES. 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. Fortunately, experiments are rapidly improving and can thus test the parameter space of the most promising theoretical models. They do this by searching for dark matter interactions with atomic nuclei or electrons in a terrestrial detector, by looking for the annihilation or decay products of dark matter in high-energy cosmic rays, and by studying the impact of dark matter on the evolution of the Universe as a whole.

However, exploiting the experimental results to their full extent requires strong theoretical efforts as well. We use experimental data to constrain theories of dark matter, and as a guideline for developing novel and improved theories of dark matter. This requires a deep understanding of the particle physics aspects of dark matter, but also of astrophysical concepts and of the physics of the early Universe.

NEUTRINOS. Our understanding of neutrinos has skyrocketed in the past two decades. Neutrino physics today is a 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.

When studying neutrino phenomenology, we focus in particular on neutrino oscillations, the periodic conversion of one neutrino flavor into another. On the one hand, we investigate the quantum mechanical underpinnings of this phenomenon, for instance the coherence conditions required for neutrino oscillations to occur. On the other hand, we make detailed predictions that can be tested in present or future neutrino oscillation experiments, we study how these experiments can distinguish between different theoretical frameworks, and we compare our predictions to experimental data. Our main tools are analytical calculations as well as numerical simulations such as GLoBES, which we use and develop as needed.

COLLIDERS, in particular the flagship of particle physics, the Large Hadron Collider (LHC). Virtually all extensions of the Standard Model involve new particles beyond the three known families of quarks and leptons, the SU(3) x SU(2) x U(1) gauge bosons, and the Higgs boson. If these new particles are not too heavy, they can be produced at the LHC, and they can be observed in the ATLAS and CMS detectors. Moreover, new particles can alter the behavior of Standard Model particles such as neutral mesons, which are studied with great precision by LHCb.

Our work in collider physics involves predicting production cross sections and decay rates for new particles, developing search strategies, validating these search strategies with realistic numerical simulations, and, wherever possible, using real data to constrain the theoretical models we study.