Search Talks

How do we weigh the Universe? Where is the Dark Matter? I will discuss these questions and show that several independent methods, including the observed present-day abundance of rich clusters , the evolution of cluster abundance with redshift, the baryon-fraction in clusters, the observed Mass-to-Light function from galaxies to superclusters, and other large-scale structure observations, all reveal a universe with a low mass density parameter of ~20% of the critical density. The data suggest that the mass in the Universe, including the dark-matter, approximately follows light on large scales and that most of the mass resides in huge dark halos around galaxies. I will review the combined observational evidence for dark-matter and for dark-energy in the universe and their cosmological implications.

The particle physics community is bubbling with excitement since the recent discovery in the cosmic radiation of a positron and electron excess at high energy. This may be the first indirect hint that dark matter particles wander in the halo of the Milky Way. However, these species do not seem to have the expected properties. I will review the various pieces of that puzzle and present a status report of the current developments in that fast moving field.

Strongly warped regions, or throats, are a common feature of string theory compactifications. In the early, hot universe, energy will be transferred between these throats and between throats and the standard model. Using the gauge-gravity duality, we calculate the rate of this energy transfer. Due to the warping, the resulting decay rate of throat-localized Kaluza-Klein states to other throats or the standard model is strongly suppressed. If their lifetime is longer than the current age of the universe, these states are an interesting dark matter candidate. We discuss a scenario along these lines.