Finite-size effects in the SS-model: two component nonlinear integral equations Original Research Article

We derive a finite set of nonlinear integral equations for describing the finite-size dependence of the ground state energy of the O(4) nonlinear sigma model. By modifying the kernel functions of these equations we propose nonlinear integral equations for the finite-size effects in the SS-model. The equations are formulated in terms of two complex valued unknown functions and they are valid for arbitrary real values of the couplings.