Special Physics Department Seminar
Dr. Gordan Krnjaic
Fellow Theoretical Physics Division
Fermi National Laboratory
Monday, August 14, 2017

Discovering or Falsifying Light Thermal Dark Matter 

This talk covers the theoretical features and experimental status of thermal dark matter (DM) with mass below the electroweak scale (M_DM << 100 GeV).  In this class of models, dark and visible matter are initially in thermal equilibrium during the early universe when the DM is relativistic (T_photons  >> M_DM). During this epoch, dark and visible matter annihilate into each other at equal rates and both number densities are calculable from equilibrium thermodynamics.  However, as Hubble expansion cools the universe, the annihilation rates fall out of equilibrium and the co-moving DM number density becomes fixed to its value when equilibrium is lost. Thus, these models predict a firm relationship between the dark-visible annihilation rate and the cosmic DM abundance, which implies a sharp sensitivity target for a variety of  novel, accelerator based search techniques. It is found that a small set of future experiments based on these new techniques can decisively discover or falsify nearly all predictive models of thermal DM below the electroweak scale.