Long-wavelength amplification of an NLS conserved-charge violation in a one-dimensional Gross-Pitaevskii-Poisson field

Abstract

Can weak self-gravity be treated as a small, generic perturbation of the integrable one-dimensional cubic nonlinear Schrödinger equation? We test this question by following the first nontrivial local NLS charge, $Q_3$. In the Gross-Pitaevskii-Poisson model it obeys the exact identity ${\dot{Q}}_3=\kappa F_3$, where $F_3$ is the instantaneous gravitational force on the charge. We quantify the initial violation through the normalized mean-square displacement of $Q_3$. Its curvature coefficient, $A_3=\mathrm{Var}(F_3)/\mathrm{Var}(Q_3)$, measures the root-mean-square initial speed of the charge in units of the charge's own ensemble width. For a UV-regulated, linearly stable Gaussian initial-data preparation, Wick contraction gives $\mathrm{Var}(Q_3)=O(L)$ and $\mathrm{Var}(F_3)=O(L^2)$, hence $A_3=O(L)$. Direct Monte Carlo evaluation of the full nonlinear observables confirms these powers for $16\le L\le 512$. The linear growth of $A_3$ means that admitting longer wavelengths makes nominally weak gravity increasingly effective at displacing the NLS charge. Along the Jeans-stable sequence ${\kappa }_L\propto L^{-2}$, the associated short-time curvature scale is $L^{3/2}$ instead of the $L^2$ benchmark of an infrared-uniform perturbation. This is an equal-time result, not a relaxation-rate or KPZ measurement. The local sound sector contains the Burgers self-coupling required for KPZ, but unscreened gravity also generates a relevant inverse-gradient coupling and, at fixed strength, a Jeans band. A dynamical connection to KPZ therefore requires a projected charge-relaxation calculation and a branch-resolved structure-factor test.

9 pages, 1 figure