Functional approach to strong-coupling theory in static models. I. Charged-scalar model

The strong-coupling theory in static models is formulated in terms of functional integrations. The method is demonstrated for the charged-scalar model. The expression of elastic and inelastic meson-nucleon scattering amplitudes is obtained to leading order in the strong-coupling expansion $\frac{1}{g}$ expansion), while the isobar energy levels are obtained up to the next to the leading order.