Conservation Laws and Sum Rules in the Heavy Quark Limit
  In the heavy quark limit, hadrons appear as eigenstates of the light degrees of freedom under the static color field of the heavy quark. In this formalism, the weak form factors appear naturally as the overlaps of the initial and final wavefunctions of the light degrees of freedom, and the Bjorken and Voloshin sum rules are statements of conservation of probability and energy. Moreover, parity conservation can lead to a sum rule which relates weak form factors at different kinematic points. {}From this sum rule, model independent lower bounds on Isgur--Wise form factors can be obtained analytically. 
Chi-Keung Chow