Cosmology of "Visible" Sterile Neutrinos

We point out that in scenarios with a low reheating temperature $T_R << 100$ MeV at the end of (the last episode of) inflation or entropy production, the abundance of sterile neutrinos becomes largely independent of their coupling to active neutrinos. Thus, cosmological bounds become less stringent than usually assumed, allowing sterile neutrinos to be ``visible'' in future experiments. For example, the sterile neutrino required by the LSND result does not have any cosmological problem within these scenarios.Comment: Talk given at the ``8th Workshop on Non-Perturbative Quantum Chromodynamics", June 7-11, 2004, Paris, France; 7 pages, 2 figure

Theory of Dark Matter

The search for dark matter is a very wide and active field of research. Many potential hints of dark matter have appeared recently which led to a burst of theoretical activity and model building. I necessarily concentrate here only in some aspects of it. I review here some recent hints and some of the ways in which they could be explained.Comment: Plenary review talk at "Physics at the LHC 2010", 7-12 June 2010, DESY, Hamburg, Germany; 6 pages, no figures, desyproc.cls file needed to typese

Experimental relevance of low reheating temperature cosmologies

Standard simple assumptions are usually made about the pre-Big Bang Nucleosynthesis epoch, from which we do not have observations. Modifying these assumptions, the predicted density of relic particles such as neutralinos and sterile neutrinos can be very different from that in the standard case. For example, neutralinos could have the dark matter density in (almost) any supersymmetric model, and sterile neutrinos with mixings large enough to be soon detected in neutrino experiments would become cosmologically acceptable. These possibilities are important in view of what the LHC, and neutrino experiments could soon find.Comment: Talk given at the 43rd Rencontres de Moriond- Cosmology, La Thuile, Italy, March 15 - 22, 2008. 4 pages, 3 figures, uses moriond.st