Dark Matter Bound States and Indirect Dark Matter Signals
Most of the mass density in our universe is not composed of the familiar particles that make up atoms. Rather it is something different that goes by the name dark matter. We have considerable evidence for dark matter, for example, through of its gravitational influence on the motion of stars. The current theory of elementary particles has no candidate for the dark matter and it is probably a new type of particle. A number of experiments search for dark matter including the direct detection experiments which look for its scattering off nuclei. Dark matter annihilation in the early universe and in our galaxy today can give rise to what are called indirect signals for the dark matter. While little is known about the particle physics properties of dark matter one possibility, that occurs in simple models, is that dark matter forms bound states analogous to the positronium states that an electron and positron form. I discuss how taking such bound states into account changes (in some regions of parameter space) our expectations for the dark matter annihilation rate and hence indirect signals for dark matter.