  The quark behaviour in the background of intensive stochastic gluon field is
studied. An approximate procedure for calculating the effective Hamiltonian is
developed and the corresponding ground state within the Hartree-Fock-Bogolyubov
approach is found. The comparative analysis of various model Hamiltonian is
given and transition to the chiral limit in the Keldysh model is discused in
detail. We study response to the process of filling up the Fermi sphere with
quarks, calculate the vacuum pressure and demonstrate the existence of
filled-in state degenerate with the vacuum one.
