On the Infrared Limit of Unconstrained SU(2) Yang-Mills Theory

The variables appropriate for the infrared limit of unconstrained SU(2) Yang-Mills field theory are obtained in the Hamiltonian formalism. It is shown how in the infrared limit an effective nonlinear sigma model type Lagrangian can be derived which out of the six physical fields involves only one of three scalar fields and two rotational fields summarized in a unit vector. Its possible relation to the effective Lagrangian proposed recently by Faddeev and Niemi is discussed.