Effects of nonlinearity in wave propagation in multicomponent Bose-Einstein condensates

We consider a spinor Bose-Einstein condensate in its polar ground state. We analyze magnetization waves of a finite amplitude and show that their nonlinear coupling to the density waves change the dependence of the frequency on the wavenumber dramatically. In contrary, the density wave propagation is much less modified by the nonlinearity effects. A similar phenomenon in a miscible two-component condensate is studied, too.