Strong coupling expansion for the ground-state functional in a model of the quantum theory of a scalar neutral field with self-interaction $g\varphi^4$ in the case of two-dimensional spacetime

It is argued that the solution of the ground-state equation (1) in the case of the strong coupling (5) can be represented by series in integral powers of the parameter $\varepsilon$, and that these series have a positive radius of convergence.