Low-energy manifestations of heavy particles: Application to the neutral current

It is argued that in broken-symmetry theories the decoupling of heavy particles is incomplete. Some possible manifestations of this effect in neutral-current processes and the decay $K_L\to \mu \mu$ are discussed. In the case of the neutral current, heavy-particle effects may be calculated accurately including strong-interaction corrections. A new method of making such calculations is explained and its application to the neutral-current process discussed in detail. The method is more efficient than previous ones and is especially useful in calculations involving several mass scales.