Effective Dynamics on a Line
  The effective classical/quantum dynamics of a particle constrained on a closed line embedded in a higher dimensional configuration space is analyzed. By considering explicit examples it is shown how different reduction mechanisms produce unequivalent dynamical behaviors. The relation with a formal treatment of the constraint is discussed. While classically it is always possible to strictly enforce the constraint by setting to zero the energy stored in the motion normal to the constraint surface, the quantum description is far more sensitive to the reduction mechanism. Not only quantum dynamics is plagued by the usual ambiguities inherent to the quantization procedure, but also in some cases the constraint's equations do not contain all the necessary information to reconstruct the effective motion. 
P. Maraner