The Dark Matter Universe

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Now that the Higgs boson - the final piece of the Standard Model of particle physics - has been discovered, particle physicists are turning to the cosmos to inspire the next great discoveries. The existence of dark matter is one of the Universe's greatest mysteries. Within a galaxy, all the visible matter - the stars and interstellar gas - are made from atoms, and yet atomic matter represents only 15%, on average, of the total mass of a galaxy. The remaining 85% is dark matter. Dark matter's presence in the Universe provides the cosmic foundation for galaxies and stars to form. However, its particle physics properties remains as yet unknown.******Dr. Tulin's research will provide a new direction in the quest to identify the dark matter particle. He proposes that galaxies and clusters of galaxies may be used as cosmic particle colliders to discover dark matter's elusive nature. This idea is similar in spirit to Rutherford's famous gold foil experiment: by studying the energy (and angular) dependence of alpha-particle scattering, the particle physics structure of the atom was discovered, being governed by the electromagnetic force.*******The same experiment can be done with dark matter in galaxies and galaxy clusters. Dark matter particles may scatter with other dark matter particles in a galaxy, which changes the how they are distributed, which in turn influences the motions of stars and gas that trace the dark matter particles' gravity. Moreover, different astrophysical scales, from the smallest dwarf galaxies to the largest clusters, have dark matter particles at different energies (with larger objects corresponding to larger energies). Therefore, combining observations from dwarfs to clusters is equivalent to tuning the dark matter "collider" to different energies. From this combination of astrophysical measurements, the properties of dark matter - such as its mass and the nature of its particle interactions - can be discovered.*******Although there is no guarantee that dark matter has a scattering interaction in galaxies, observations of dwarf galaxies, low surface brightness spiral galaxies, and galaxy clusters suggest that their structure is incompatible with forming by the gravitational collapse of dark matter particles that have no particle interactions. Moreover, the same particle physics giving a scattering interaction can also explain why dark matter exists in the Universe today (that is, how it was produced and why it is stable).*******Dr. Tulin's research will provide a theoretical framework, based on statistical mechanics for dark matter particles, for extracting microscopic dark matter properties from macroscopic observations of stellar and gas dynamics. He will explore the particle physics implications for dark matter and propose new models that can be connected to astrophysical observations, as well as address complementarity with searches for dark matter and other dark particles in laboratory experiments.*** **