  We propose a new version of SU(N) Yang-Mills theory reformulated in terms of
new field variables which are obtained by a nonlinear change of variables from
the original Yang-Mills gauge field. The reformulated Yang-Mills theory enables
us to study the low-energy dynamics by explicitly extracting the topological
degrees of freedom such as magnetic monopoles and vortices to clarify the
mechanism for quark confinement.
  The dual superconductivity in Yang-Mills theory is understood in a
gauge-invariant manner, as demonstrated recently by a non-Abelian Stokes
theorem for the Wilson loop operator, although the basic idea of this
reformulation is based on the Cho-Faddeev-Niemi decomposition of the gauge
potential.
