  We perform a lattice analysis of the Faddeev-Niemi effective action
conjectured to describe the low energy sector of SU(2) Yang-Mills theory. We
generalize the effective action such that it contains all operators built from
a unit color vector field n with O(3)-symmetry and maximally four derivatives.
To avoid the presence of Goldstone bosons, we include explicit symmetry
breaking terms parametrized by an external field h of mass-dimension two. We
find a mass gap of the order of 1.5 GeV.
