  Recently, the concept of dynamical extended charged events has been
introduced, and it has been argued that they should play as central a role as
that played by particles or ordinary branes. In this article we show that in
the presence of a Chern-Simons coupling, a magnetically charged extended event
emits an extended object, which geometrically is just like a Dirac string, but
it is observable, obeys equations of motion, and may be electrically charged.
We write a complete action principle which accounts for this effect. The action
involves two Chern-Simons terms, one integrated over spacetime and the other
integrated over the worldvolume of the submanifold that is the union of the
Dirac world-sheet and the history of the emitted physical object. By demanding
that the total charge emitted by a composite extended magnetic event be
quantized according to Dirac's rule, we find a quantization condition for the
Chern-Simons coupling. For a 1-form electric potential in D=2n+1 spacetime
dimensions, the composite event is formed by n elementary extended magnetic
events separated in time such that the product of their transverse spaces,
together with the time axis, is the entire spacetime. We show that the emitted
electric charge is given by the integral of the (n-1)-th exterior power of the
electromagnetic field strength over the last elementary event, or,
equivalently, over an appropriate closed surface. The extension to more general
p-form potentials and higher dimensions is also discussed. For the case D=11,
p=3, our result for the quantization of the Chern-Simons coupling was obtained
previously in the context of M-theory, a remarkable agreement that makes the
existence of events even more compelling.
