  The Wick rotation provides the standard technique of computing Feynman
diagrams by means of Euclidean propagators. Let us suppose that quantum fields
in an interaction zone are really Euclidean. In contrast with the well-known
Euclidean field theory dealing with the Wightman and Schwinger functions of
free quantum fields, we address complete Green's functions of interacting
fields, i.e., causal forms on the Borchers algebra of quantum fields. They are
the Laplace transform of the Euclidean states obeying a certain condition. If
Euclidean states of a quantum field system, e.g., quarks do not satisfy this
condition, this system fails to possess Green's functions and, consequently,
the S-matrix. One therefore may conclude that it is not observed in the
Minkowski space.
