The O(N) Nonlinear Sigma Model in the Functional Schr\"{o}dinger Picture

We present a functional Schr\"{o}dinger picture formalism of the (1+1)-dimensional $O(N)$ nonlinear sigma model. The energy density has been calculated to two-loop order using the wave functional of a gaussian form, and from which the nonperturbative mass gap of the boson fields has been obtained. The functional Schr\"{o}dinger picture approach combined with the variational technique is shownto describe the characteristics of the ground state of the nonlinear sigma model in a transparent way.