“…The nonlinear Klein-Gordon equation has then become a popular superfluid model, which is able to cover the entire velocity range, especially the relativistic region [28,55,31,39,53,54,15,48,23,49,21,52]. As a model for describing a rotating galaxy in Minkowski metric, the nonlinear Klein-Gordon equation in a rotating frame [28,31,39,53,54] is used. Also, the nonlinear Klein-Gordon equation appears as a relativistic generalization of the Gross-Pitaevskii equation, a nonlinear Schrödinger equation that serves as a basic model for Bose-Einstein Condensates [2], also in the rotating case, see e.g.…”