  The scalar-spinor interaction Lagrangian is presented by the Yukawa
potential. In dS ambient space formalism, the interaction Lagrangian of
scalar-spinor fields was obtained from a new transformation which is very
similar to the guage theory. The interaction of massless minimally coupled
scalar and spinor fields was investigated. The Minkowski limit of the massless
minimally coupled scalar field and massive spinor field interaction in the
ambient space formalism of de Sitter space time is calculated. The interaction
Lagrangian and massless minimally coupled scalar field in the null curvature
limit become zero and the local transformation in the null curvature limit
become a constant phase transformation and the interaction in this limit become
zero. The covariant derivative reduces to ordinary derivative too. Then we
conclude that this interaction is due to the curvature of space time and then
the massless minimally coupled scalar field may be a part of a gravitational
field.
