Collisionless, less Collisionless and Collisional Matter in the Universe

Mark Vogelsberger

December 07, 2011

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Abstract: LCDM is a successful theory on large scales, but the elusive dark matter particle still has to be detected. I will discuss recent advances on understanding the fine-grained structure of collisionless dark matter and how it affects direct and indirect search experiments. In the second part of my talk I will show that despite the progress of LCDM on large scales, modeling the Universe on smaller scales is still an outstanding problem. Understanding these scales requires the inclusion of the collisional baryonic component in structure formation simulations. I will demonstrate that solving the underlying hydrodynamics equations reliably is crucial, and that uncertainties in the numerical scheme can propagate even into large scale predictions of the baryonic Universe. Towards the end of my talk I will focus on one specific small scale problem and discuss why strongly self-interacting DM becomes again an attractive alternative to standard CDM, and how it can solve some of the current problems with too collisionless dark matter.