Dynamics of a dark soliton in a curved 1D Bose-Einstein condensate
We investigate the nonlinear dynamics of dark solitons in a one-dimensional Bose-Einstein condensate confined to a curved geometry. Using the Gross-Pitaevskii equation in curvilinear coordinates and a perturbative expansion in the local curvature, we derive a set of coupled evolution equations for the soliton velocity and the curvature. For the case of constant curvature, such as circular geometries, the soliton dynamics is governed solely by the initial velocity and curvature. Remarkably, the soliton travels a nearly constant angular trajectory across two orders of magnitude in curvature, suggesting an emergent conserved quantity, independent of its initial velocity. We extend our analysis to elliptical trajectories with spatially varying curvature and show that soliton dynamics remain determined by the local curvature profile. In these cases, the model of effective constant curvature describes accurately the dynamics given the local curvature has smooth variation. When the soliton crosses regions of rapid curvature variation and/or non-monotonic behavior, the model fails to describe to soliton dynamics, although the overall behavior can still be fully mapped to the curvature profile. Our results provide a quantitative framework for understanding the role of geometry in soliton dynamics and pave the way for future studies of nonlinear excitations in curved quantum systems.