Diverging probability density functions for flat-top solitary waves

We investigate the statistics of flat-top solitary wave parameters in the presence of weak multiplicative dissipative disorder. We consider first propagation of solitary waves of the cubic-quintic nonlinear Schr\"odinger equation (CQNLSE) in the presence of disorder in the cubic nonlinear gain. We show by a perturbative analytic calculation and by Monte Carlo simulations that the probability density function (PDF) of the amplitude $\eta$ exhibits loglognormal divergence near the maximum possible amplitude $\eta_{m}$, a behavior that is similar to the one observed earlier for disorder in the linear gain [A. Peleg et al., Phys. Rev. E {\bf 72}, 027203 (2005)]. We relate the loglognormal divergence of the amplitude PDF to the super-exponential approach of $\eta$ to $\eta_{m}$ in the corresponding deterministic model with linear/nonlinear gain. Furthermore, for solitary waves of the derivative CQNLSE with weak disorder in the linear gain both the amplitude and the group velocity $\beta$ become random. We therefore study analytically and by Monte Carlo simulations the PDF of the parameter $p$, where $p=\eta/(1-\varepsilon_s\beta/2)$ and $\varepsilon_s$ is the self-steepening coefficient. Our analytic calculations and numerical simulations show that the PDF of $p$ is loglognormally divergent near the maximum $p$-value.
Comment: 9 pages, 6 figures. Submitted to Phys. Rev. E