  In an Abelian projection SU(2) gluodynamics contains Abelian gauge fields
(diagonal degrees of freedom) and Abelian matter fields (off-diagonal degrees).
The matter fields are essential for the breaking of the adjoint string. We
obtain numerically the effective action of the Abelian fields in quenched SU(2)
QCD and show that the Abelian matter fields provide an essential contribution
to the total action even in the infrared region.
