Duality, Multi-Monopole Dynamics & Quantum Threshold Bound States

Dynamics of many supersymmetric monopoles are studied in the low energy approximation. A conjecture for the exact moduli space metric is given for all collections of fundamental monopoles of distinct type, and various partial confirmations of the conjecture are discussed. Upon the quantization of the resulting multi-monopole dynamics in the context of $N=4$ supersymmetric Yang-Mills-Higgs theories, one recovers the missing magnetic states that are dual to some of the massive vector mesons. A generalization to monopoles with nonabelian charges is also discussed.