  Here I establish the field perturbation theory of pseudogaps in HTSC. The
proposed ground state suggests an internal particle-hole field, which is normal
to nesting surfaces, and having twice the Fermi wave-number. It is proved that
the system violates momentum conservation by the wave-vector of this internal
field. This violation applies to the quasi-particle propagators, as well as to
the interactions. Interaction vertices via the Pauli matrix- are established.
This, in turn, establishes the validity of the pseudogap Hartree self-energy.
