  An emergence of magnetic boson of instantonic nature, that provides a
Cooper-'pairing glue', is considered in the repulsive 'nested' Hubbard model of
superconducting cuprates. It is demonstrated, that antiferromagnetic instantons
of a spin density wave type may have negative energy due to coupling with
Cooper pair condensate. A set of Eliashberg-like equations is derived and
solved self-consistently, proving the above suggestion. An instantonic
propagator plays the role of Green function of pairing 'glue' boson.
Simultaneously, the instantons defy condensation of the mean-field SDW order.
We had previously demonstrated in analytical form \cite{2,3,4} that periodic
chain of instanton-anti-instanton pairs along the axis of Matsubara time has
zero scattering cross section for weakly perturbing external probes, like
neutrons, etc., thus representing a 'hidden order'. Hence, the two competing
orders, superconducting and antiferromagnetic, may coexist (below some Tc) in
the form of mean-field superconducting order, coupled to 'hidden'
antiferromagnetic one. This new picture is discussed in relation with the
mechanism of high temperature superconductivity.
