Supersymmetry

Many physicists have developed theories of supersymmetry, particularly in the context of Grand Unified Theories. The supersymmetric theories postulate that every particle we observe has a massive "shadow" particle partner. For example, for every quark there may be a so-called "squark" tagging along.

No supersymmetric particle has yet been seen, but experiments underway at CERN are searching for the partner of the W boson, and experiments at Fermilab are looking for the partners of the quarks and gluons. ATLAS will have tremendous capabilities to search for a broad variety of supersymetric particles.

One of the supersymmetric particles (the "neutralino") might make up the missing dark matter in the universe.