  The model of nonperturbative vacuum in SU(2) Yang-Mills theory coupled to a
nonlinear spinor field is suggested. By analogy with Abelian magnetic monopole
dominance in quantum chromodynamics, it is assumed that the dominant
contribution to such vacuum is coming from quasiparticles described by
dipolelike solutions existing in this theory. Using an assumption of the
behavior of the number density of quasiparticles whose energy approaches
infinity, we derive an approximate expression for the energy density of such
nonperturbative vacuum, which turns out to be finite, unlike an infinite energy
density of perturbative vacuum. Using characteristic values of the parameters
appearing in the expression for the nonperturbative energy density, it is shown
that this density may be of the order of the energy density associated with
Einstein's cosmological constant. The physical interpretation of the spinor
field self-coupling constant as a characteristic distance between
quasiparticles is suggested. The questions of experimental verification of the
nonperturbative vacuum model under consideration and of determining its
pressure are briefly discussed.
