all projects tagged dark matter

axion dark matter


Axions and axion-like particles are an interesting alternative to dark matter on the TeV-scale and should show new phenomena on small scales. Their very light masses cause their wave function to have de Broglie-wavelengths comparable to the size of cosmological objects such as dwarf galaxies, with less substructure on small scales and a density core as a natural consequence. With T. Schwetz-Mangold (KIT) and J. Jaeckel (Heidelberg) we are investigating signatures of axion dark matter. This requires to do quantum mechanics in gravitational fields and find analogues to classical concepts like gravitational collapse or virialisation for quantum mechanical, self-gravitating systems.

spherical collapse


Spherical collapse of a halo is one of the few instances where the fully nonlinear, relativistic equations of motion can be solved. In particular, our group has worked on collapse in non-standard gravitational models and computed the influence of tidal shear fields, split up into shear and vorticity, on the collapse dynamics. The overdensity needed for spherical collapse allows the prediction of number densities of expected haloes in a cosmic volume, and constraints on cosmological parameters as well as on the gravitational interaction from that quantity.



The Sunyaev-Zel’dovich effect describes a tiny transfer of thermal or kinetic energy from the hot intra-cluster medium of a galaxy cluster to the cold cosmic microwave background. It is a tool for detecting clusters of galaxies out to very high redshift, and provides a diagnostic of the relationship between temperature and mass of clusters. In addition, the kinetic Sunyaev-Zel’dovich effect arises due to a minuscule transfer of kinetic energy from the galaxy cluster’s electrons to the CMB photons, if the cluster is not at rest in a frame in which the CMB appears isotropic.