The expansion of the universe and the formation of cosmic structures are a testbed for the properties of gravity on the largest scales, where new and unexpected gravitational phenomena might arise and deviations from general relativity can be observed. Dark energy can drive the late-time accelerated expansion of the universe and be a viable alternative to the cosmological constant, and alternative theories of gravity can challenge our understanding of the construction principles of field theories. We aim to test these theories with data of the European Euclid satellite mission, which will carry out a 3-dimensional survey of the cosmic matter distribution and is capable of testing cosmological models beyond the standard picture. We develop and test modified theories of gravity and probe the expansion history of the universe in model-independent ways.
Physical processes in the universe probe the laws of nature on a very high energy scale and link the physics of gravity and of inflation to particle physics and the standard model. We investigate inflationary models, their relation very light elementary particles such as neutrinos and axions, the genesis of baryons and leptons in the early universe, deduce observable consequences of processes near the Planck-scale and describe early universe-physics in different frames. In particular, methods of renormalisation allow us to compute the running of fundamental constants of nature in their cosmological evolution.
Structures with very low amplitude were created probably by inflation in the early universe. They developed into the pronounced structures observed in our cosmic environment, such as galaxies, galaxy clusters, large-scale filaments, and huge regions devoid of matter. Understanding the non-linear, non-equilibrium evolution of these structures is important not only to interpret cosmological observations correctly, but also to understand the fundamental reasons for the appearance and the internal constitution of these structures. We are developing a kinetic field theory for cosmic structure formation, which is formally and conceptually close to statistical quantum-field theory.
Groups: Prof. Matthias Bartelmann, Prof. Lavinia Heisenberg