BPS Equations, BPS States, and Central Charge of N=2 Supersymmetric Gauge Theories

We derive the central charge and BPS equations from the low-energy effective action for N=2 SU(2) Yang-Mills theory in the Coulomb phase, using a systematic, canonical procedure. We then obtain solutions for monopole and dyon BPS states, whose core structure is described by a dual Lagrangian containing the monopole or dyon as a fundamental field. Spherically symmetric states possess a shell of charge at a characteristic radius.