Fredagskollokvium: Torsten Bringmann: Identifying the particle nature of dark matter: from the distribution of matter at small scales to cosmic ray observations

The leading candidate for the observed cosmological dark matter (DM) is a new type of 
weakly interacting massive particle (WIMP) which is thermally produced in the early 
universe. Its decoupling from the thermal bath, however, does not only set the observed 
DM relic density today but also imprints a small-scale cutoff in the spectrum of primordial 
density fluctuations, corresponding to the least massive protohalos that can form. A dark 
force between the WIMPs could further modify the matter distribution at small scales. 
The clustering of (dark) matter thus potentially provides valuable information about the 
WIMP particle nature, fully complementary to more traditional ways of searching for DM.

The second part of the talk will focus on one of those more traditional methods, intrinsically 
connected to the way DM clusters: indirect searches aim at identifying a possible 
contribution from DM self-annihilation or decay to the observed flux in cosmic rays. Special 
emphasis is put on the basic principles and current status of observations in gamma rays,
the 'golden channel' of this technique, but I will also comment about what the apparently 
anomalous high-energy rise in the cosmic ray positron fraction can tell us about the nature 
of DM.