  The possibility for occurrence of a Bose condensate of dibaryons in nuclear
matter is investigated within the framework of the Walecka model in the
mean-field approximation. Constraints for the omega - and sigma - meson
coupling constants with dibaryons following from the requirement of stability
of dibaryon matter against compression are derived and the effect of sigma -
and pi - meson exchange current contributions to the sigma - dibaryon coupling
constant is discussed. The mean-field solutions of the model are constructed.
The effective nucleon mass vanishes when the density of dibaryons approaches a
critical value about 0.15/fm^3. The Green's functions of the equilibrium binary
mixture of nucleons and dibaryons are constructed by solving the Gorkov-Dyson
system of equations in the no-loop approximation. We find that when the square
of the sound velocity is positive, the dispersion laws for all elementary
excitations of the system are real functions. This indicates stability of the
ground state of the heterophase nucleon-dibaryon mixture. In the model
considered, production of dibaryons becomes energetically favorable at higher
densities as compared to estimates based on a model of non-interacting nucleons
and dibaryons.
