Long-time limit studies of an obstruction in the g-function mechanism for semiclassical focusing NLS

We consider the long-time properties of the an obstruction in the Riemann-Hilbert approach to one dimensional focusing Nonlinear Schrodinger equation in the semiclassical limit for a one parameter family of initial conditions. For certain values of the parameter a large number of solitons in the system interfere with the $g$-function mechanism in the steepest descent to oscillatory Riemann-Hilbert problems. The obstruction prevents the Riemann-Hilbert analysis in a region in $(x,t)$ plane. We obtain the long time asymptotics of the boundary of the region (obstruction curve). As $ttoinfty$ the obstruction curve has a vertical asymptotes $x=pm ln 2$. The asymptotic analysis is supported with numerical results.