Integrable model of a nonlinear complex scalar field with nontrivial asymptotic behavior of soliton solutions

The field theory model in two-dimensional space-time with the Lagrangiaa
$$ L=\frac{\vert\partial_{\mu}\psi\vert^2}{1-\lambda^2\vert\psi\vert^2}+m^2(\vert\psi\vert^2-\lambda^{-2}) $$
is studied. It is a completely integrable Hamiltonian system. The explicit form of $N$-soliton solutions with asymptotic behavior $\vert\psi\vert\to\lambda^{-1}$ as $\vert x\vert\to\infty$ is found.