Possible creation of net circular polarization and not only   depolarization of spectral lines by isotropic collisions
  We will show that isotropic collisions of electrons and protons with neutral hydrogen can lead to creation of net orientation of the atomic levels in the presence of a magnetic field. Consequently, the emitted Stokes-V profile of the spectral lines can be almost symmetric in contrast to the typical antisymmetric signature of the Zeeman effect. Moreover, the amplitude of the symmetric lobe can be significantly higher than the amplitude of the antisymmetric components. This mechanism is caused by a $\pm{M}$ symmetry breaking of the collisional transitions between different Zeeman sublevels. We will show an example of our first results for the H$\alpha$ line. This new mechanism could perhaps explain the net circular polarization of spectral lines observed in some solar limb observations and which are currently not understood. However, our results are very preliminary and more developments are needed for going further on. 
Jiri Stepan, Sylvie Sahal-Brechot