Theory Seminar October 18 Prof. Micheal Berger (hosted by Alford) Indiana University Interacting Dark Energy and the Expansion History of the Universe Recent observations indicate that the Universe has entered a period of accelerated expansion. This behavior is adequately described by adding a very small cosmological constant to Einstein's equation. However there is not a good theoretical understanding for the size of this constant which seems to be related to a length scale that is the geometric average of the Planck length and the current size of the observable Universe. We will review the basic formalism describing the expansion of the Universe, then present an alternative model involving a dark energy that decays into matter. This model gives a similar good fit to the expansion history of the Universe. Coffee: 2:30 PM, 241 Compton         Lecture: 3:00 PM, 241 Compton