Introduction to the Heavy Quark Effective Theory

Heavy Quark Effective Theory (HQET) is a new approach to QCD problems involving a heavy quark. In the leading approximation, the heavy quark is considered as a static source of the gluon field; 1/m corrections can be systematically included in the perturbation theory. New symmetry properties not apparent in QCD appear in HQET. They are used, in particular, to obtain relations among heavy hadron form factors. HQET also simplifies lattice simulation and sum rules analysis of heavy hadrons.