3.2. Accretion of Angular Momentum
There is evidence that galaxies from time to time acquire material with significantly different alignment of angular momentum. Polar rings and counterrotating components in disks are clear examples.
If this such accretion continuously alters the orientation of the dark halo angular momentum axis, the disk finds itself in a slowly changing potential, in which it is continuously trying to align itself with the dark halo symmetry plane. Damping is now not such a problem, as the halo is continuously changing in response to outside influences, rather than only to the disk. As shown by Jiang & Binney (1999), this process can generate realistic warp amplitudes in disks.
If this mechanism dominates, one might expect this slowly changing tidal fields to result in rather symmetric warps, though no detailed simulations have yet been performed.